Why does the hegemon sabotage the other imperialist powers when it also has money invested in those countries?
So the bourgeoisie have money invested in all countries, so no matter who win or loses, they make a profit. However, the USA sabotages other imperialist powers to keep its status as a hegemon, but why does it do that when it doesn’t really matter which imperialist is the hegemon when all the bourgeoisie make profit regardless?
This is covered in Lenin's Imperialism: The highest stage of capitalism. To paraphrase, the bourgeoisie is not a homogeneous group, especially across borders. They are in competition with the bourgeoisie of their nation and other nations for their share of wealth too.
Hopefully someone will give a more well sourced answer as I don't have time to look up the passages from the text right now.
Yes, the military-industrial complex is a quite powerful industry. Also, note that capitalism doesn’t necessarily advocate logical decisions — socialism would be better for everyone even in a selfish perspective, because oppressed people might be inventing things like cures for cancer that even the bourgeoisie want…