Economic buildings
Cities increase the value of safe territory by raising the population ceiling. Factories improve recovery and make repeated attacks less punishing.
Place economic structures behind stable borders. If a structure can be captured immediately, it is usually better to spend troops defending or expanding first.
Defensive buildings
Defense posts are strongest at chokepoints, mountain exits, and borders where a strong player is likely to test you. They are weaker when scattered randomly across quiet land.
SAM networks matter once missiles and nuclear weapons appear. A single SAM is not a guarantee; coverage and spacing matter more than one expensive point defense.
Naval infrastructure
Ports are not just travel points. They decide whether you can contest ocean control, land troops safely, and threaten islands or distant continents.
A player without a port can become trapped even with a strong land army.