If you want power over another country, attacking them is a very inefficient path. You will take losses, and you won't be able to take their resources intact. The easier and cheaper method is to just bribe their leaders into selling you whatever you want.

The US starts wars even when it doesn't need to, because there are a handful of companies that stand to make a lot of money selling weapons. No other country has such a large and influential military lobby, so other countries tend not to start wars for private profit.

Except imperialism is actually incredibly inefficient in the long term. Western nations become imperialist due to the contradictions created by capitalism.There is a reason why China's foreign policy is centered around mutual advancement.