Perfect defence is widely recognised as the best strategy. As of now, it gives infantry a -10 for price and a + for defence while nerfing all the main attack units. Edit

==== Directly copied from the forums
1. General style of playing for the strategy
Play defensive, what's in the name , and keep spamming infantry. Don't build any other units except infantry, it's a waste of money if you buy other units (only transports or maybe 1 bomber for turnblock). You need to play the defensive way, never lose a capital city you take. Keep expanding when possible, and build a defenceline around every capital city you take. When a defenceline is destroyed by the enemy; move all your nearby troops in the city, so the enemy will lose there. Also restore the wall at the same time, so you can do a counter attack the next turn. PD has always units for attack; try to use them 1week before the reïnforcements, so it's very hard for the opponent to take it back.

2a. Strong points
- Very, very powerfull in defence (a tank general for example will lose on a 1:1 ratio to your infantry: But infantry costs $40, Tanks more then $100, same with Bombers)
- Even though it has been nerfed, it's still mobile. With (cheap) airtransports you can move around and keep pressure on the enemy
- No real money issues, It's always possible to reinforce and most times it's even possible to reinforce in all your cities within 2 turns. That makes you army bigger and bigger then the enemy; witch cannot afford that much units.
- A PD player is never defeated; unless he's really lost. Even when it looks real worse, when a PD player has country's, it can always fight back and defend well.

2b. Weak points
- Large groups are needed to make real impact therefore:
- It cannot attack on more fronts at the same time
- You need to take your time to build up your defence well (defence lines), and you need to move a lot of units. Therefor 2mins is most times not enough for a CW or for a normal game when you have a lot of territory.
- Weak against GW (see point 3)

3. The ways to oppose different kinds of strategies in a 1 v 1 match
Doesn't work good aganst GW; because a GW player attack on serval places at the same time and can destory many walls in 1 turn, so you don't know in what city the next attack will be. GW also can play on much fronts, PD can't. GW is able to create total chaos; what is disastrous for a PD player. GW > PD
Also against IF will not be easy; IF can hold on the pressure and cap territory at the same time. It's very difficult for PD to expand then, because it has to care for defence too much.
Works very good against all other strats. I think i can say that i've never been beated in a 1on1 by some other strategy then GW or IF. 

4. The role of this strategies in a 3 v 3 CW match in the team (perhaps for different kind of combinations).
Works even better in CW's then in 1on1. Because the enemy will not focus on only the PD player, he's able to keep expanding and keep attacking. A PD player will most times be the last one that is defeated when losing, or will be the player that will give the final attack when winning. Also a PD player is able to give good defending support, but is weaker in attacking. It's also not a very agressive strategy; should only used by 1player, when playing a 3v3. When playing in front, PD can hold off the enemy pretty well. When playing in the back, PD can give good attacking/defending support and is able to give money to teammates.

The choice will be different in all situation, depending on map and funds:
- When playing 1v1 europe 5k: Greece and Ukraine are the best options: You can expand in the first turn to: Turkey, Italy or Romania and Bulgaria (from greece).
- When playing 1v1 europe 10k: Turkey and Ukraine are the best options
- When playing in a teamgame, you should start somewhere east: Or (if 10k) take Germany/Spain to hold of the opponent.
East europe is better in Europe maps, because you have cities close to expand. Starting in Spain should be an option, but the enemy can hold you off there with bombers and blocking while expanding himself in the east (in case of a 1v1). A good reason to start in the west is because of the money. But PD doesn't really need much money because of the cheap units; therfore it's better to start east. Also, the +100 cities function give an advantage to PD as you have more starting units witch you can use directly.

- If Eurasia 10K usual game: I usually take South-Korea (and expand to Japan, China), Pakistan (and expand to India ans Iran) or somewhere in europe (Turkey, UK for example). 
If you have great parts in Asia with PD, that makes you almost unbeatable, because you can use your autobuy function and spam your opponent a huge unstoppable load of infantry that keeps on comming.

Never attack enemies cities in the reinforcement week, instead, reinforce your frontiers and wait it to be attacked;

Expand neutrals as much as you can, since it's easier to you to capture and defend it than wait for your enemy to try an attack;

Avoid using tanks and destroyers, instead keep spamming infantries and some bombers to support you with breaking walls and transports to expand faster;

If you have a big stack, always try to protect it with walls, since you can easily be turnblocked if you don't;

If your enemy is playing an offensive strategy sometimes it's better to "left" your cities unprotected and let them attack it, so your defense will do the work.

Please note that your situation and mindset might be different than mine, so results will be different. I just want a person to be as efficient as possible.

1. Upgrades
When playing with PD, you should consider getting the following upgrades in this order:
1. Transport Capacity, 2. Faster Infantry, 3. Air Transport 1&2, 4. Cheaper Infantry, 5. Lucky Infantry, 6. General's Infantry Attack, 7. General Movement, 8. Faster General 1&2, 9. Cheap Transport, 10. Safer Transport. 
When you have all these upgrades, you will be able to utilize PD in ways people won't expect.

2. General Rules to Follow
I prefer to start with a country that has at least 1 port city. Why? Because having 1 port city allow you to expand twice as fast for half the cost. If you choose to pick a land lock area, you will eventually need to buy an air transport to keep up with expansion of your enemy. Learn how to use 1 transport to move 6-10 units instead of buy 2.

90% of your army should be infantry, 9.99% should be logistic units like air transport and sea transport. 0.01% other. This mean I should not see a tank army if you are pd. That 0.01% is your small force used to break walls.

There are 8 infantry units in neutral France, you will need 16 infantry to take it. As a general rule of thumb, you will need double the infantry to capture an infantry defended city. If they are militia, you will need the total plus 1 more infantry. If you see an enemy army, and you can't crush it, either prepare to defend, or move on. Don't suicide your weak attacking infantry.

Wall every capitol you have. Wall every city that has 3+ reinforcement. Money is not an issue, but reinforcement is.

3. PD Tactics
Now here is the interesting part: how to play an unstoppable pd. When playing pd, you must understand the basic tenant that you are weak; therefore, you need to slow down your opponents by creating walls. Wall a city before you take it, wall the entire middle east, walls everywhere. You have lots of infantry you can spare, now use them for your walls.

Now that you have a strong outer shell, move all your units quickly from the heart to the front lines using various air transport and sea transport. You should be able to move great distance by building a train system. Do not worry about how fast your enemy is expanding, just make sure your unit count matches his or is greater. (Unless you are pro, in which case don't let his unit count become 2x greater than yours.)

They are some people who like to say this beats that, or SM is superior, but I am here to tell you that there is no such thing. This isn't rock-paper-scissor. If you have a better mind, you will win. With that being said, the way to generally beat gw is by wall everything. The entire middle east wall, he will generally not have defense, so make sure you use your air transport to out expand him while slowing him down with massive and elaborate walls. Create elaborate palace (double walls). SM will have less units then you, but make sure you can move unit quickly like he can. Against another PD user, you must first wall the city, then attack it. When you are playing against a GC user, make sure you are smart enough to crush his tank/combo stacks by defending, and you will win.

When you are about to capture a city, make sure you wall it also, so you can use your troops immediately. This tactic applies to all strats. Don't be lazy, wall everything.

4. Playing PD in Europe
If the place is crowded, stay compact so you can maximize your stack. If not crowded, expand as fast as possible. (10k) Good choices for PD in western europe are UK, France, Germany, Spain, while Italy is risky. (10k)Eastern europe, would be turkey, russia central, and some would say ukraine. I prefer starting in western europe, germany. They may be other good starting countries, but that dials down to the player preference and the condition of the match.

5. Playing PD in Asia
Generally, you should start places that have great amount of starting units, and attack capitols that has militia. (10k) Starting, good choices north asia would be china north, china northeast, south korea. South asia, I prefer burma.

(10k)Playing PD in the middle east is risky, because normally you will have a 2 sided war and you don't have enough resources to fund and move units efficiently. However, if you do choose to play in the middle east, you should pick pakistan, and hope your ally loves you enough to fund you for your war.

6. Playing PD in America
In North america, starting anywhere on the east coast USA is a safe bet. Grab the entire coast and slowly expand westward and south. However, if want to play in SA, i suggest picking Colombia and moving upward towards the US and expand south for cash simultaneously. 

7. Playing PD across the ocean
Some people might say pd can't attack across the ocean, but they are wrong. You put lots of infantry, perhaps 100-200 onto transports, build a couple destroyers, and every turn, you move your transport and build a destroyer wall around the transport. You don't have to attack head on. You can attack africa and work up, be creative, and you will win. I want to stress the importance playing creatively. 

Closing Note
Remember, when playing PD, don't expect a fast victory. You play by overwhelming your opponents by troops, you play to crush them with your endless stacks of infantry.
There is a secret to win with PD, the answer is logistics.

In world games, once fully expanded (full continent etc..) there's nothing wrong with making tanks, bombers, or even marines in subs to invade unexpectedly. What I usually do is start by setting up my defense walls, and spamming infantry in cities to destroy all enemies who wish to attempt invading. Once I'm set up, I make subs and marines to invade a continent, along with a large stack of infantry in naval transports (with destroyers/bombers to defend.) I take as many cities as I can 1 week before reinforcements with my marines, and the next week I replenish my new cities with the large amount of inf I brought along. Once that process is executed properly, you've won afterwind. ====