1) Research:
Research is really important in this game because it gives your troops more strength. Start with researching infantry and armored cars. Infantry will unlock the other infantry units. Armored cars will unlock the other armored units. After that, I usually research artillery and light tanks. After that, interceptors and destroyers and/or submarines. I prefer not to invest in militia because they cost a lot of manpower, have high daily upkeep, and low offensive strength. When they are available, I usually ditch the light tanks and research medium tanks. With medium tanks, you will easily beat players that produce light tanks. They are much more powerful than light tanks are barely cost more. Also, make sure to research motorized infantry. They are also very powerful.
2) Construction:
Start with building one of these in each city: Barracks, Ordinance Foundry, Tank Plant, Aircraft Factory, and Naval Base. If you don't have a coastline, you can build a second Barracks, Ordinance Foundry, Tank Plant, or Aircraft Factory. Alternatively, you can build a secret lab, but you won't need that until later. If you can spare the resources, then also build industry in each core city. It is highly recommended to build industry early on in provinces with the double resource production icon as those provinces have double production. It is also highly recommended to build industry in provinces that produce resources that you lack. You can easily beat your neighbors economy-wise if you build industry. Remember, level one industry gives a 10% boost to production, level two 25%, all the way level five which gives a 100% boost to production. I also like to build recruiting offices alongside industry so I have enough manpower. This is highly recommended in the Allies doctrine where you often lack resources.
3) Troops:
Don't produce infantry as you start already with enough of them and you don't want to have a problem with food consumption a bit later in the game. In your tank city, first produce light tanks, then medium tanks. In your barracks city, don't produce anything until you research motorized infantry, then produce motorized infantry. In your ordinance city, rotate production between anti-tank, artillery, and anti-air. When SP Artillery and SP Anti-Air are researched, produce those instead of artillery and anti-air. In your aircraft city, build interceptors as scouts. After you research tactical and attack bombers, build those, as they deal damage while getting little back(except when your opponent has anti-air). What you do in your naval city depends on your opponent. If you opponent is building subs, build destroyers, opponent building destroyers, build battleships, opponent building battleships, build subs.
4) Attack AI:
On day 2 you can attack AI (computer players). Group your units together and line them up along the border. Have at least 12 units along the border, but to be safe you can have as many as 20. You can prevent revolts by capturing the capital last, it will raise your morale by 10%. The pro of attacking AI is that it will give you more production(through the morale boost and the extra city). The con is that another player might attack you while you are attacking the AI. Make sure you have units left behind to protect your important provinces from player attack.
5) Attack Players:
On day 4, you are now ready to attack a player. Do the same thing you did the AI, this time with more units. Make sure you have at least 30 units attacking. Important: Before you attack a player click on the "I" in the diplomacy menu to see the level and the stats of that player. If he is a good player you might want him as an ally rather than an enemy. If you want to play aggressively, you can attack a player on day one. Just make sure that you take out his cities before he has produced any units.
Sidenote:
Knowledge is power. Read the newspaper to see who is at war with who. If two players are in a war and you see in the newspaper that they both are taking huge losses you might want to invade when the fight is almost over and take everything.
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