In order to produce new units you have to research them first.

5.2 Allocate missing victory points faster than your enemies.

4.10 Make use of Premium Account features.

4.9 Consider playing Call of War on multiple platforms.

4.7 Check your front reports and notifications.

4.6 Consider constructing new production buildings in conquered provinces.

4.4 Upgrade your core provinces to the maximum.4.2 Keep conquering and eliminating threats.4.1 Keep researching, producing and upgrading your units.3.15 Don’t forget about stealth and scouting.3.9 Gather advanced information about other countries.3.8 Build Infrastructure on select supply routes.3.5 Upgrade your units on the battlefield.3.4 Upgrade your unit production buildings.2.13 Use the Wiki, FAQ forum and help chat.

2.12 Grant small AI nations Right of Way or Shared Map.2.7 Select your first target and rally your troops at the border.2.6 Scout out hostile neighbors and potential targets with your troops.2.5 Contact other players and find allies.2.4 Produce units in your production buildings.2.3 Construct buildings for unit production in your urban provinces.

World conqueror 4 beginners guide