I heard that capitalism is the cause of militarism and war, but I don't understand why that wouldn't continue under socialism?

I heard that monopoly capitalists competing over access to resources and markets caused the world wars. And subsequent imperialist wars have been fought to ensure big transnational capitalists unfettered access to resources and markets in the periphery. Of course there has also been war between peripheral countries, and I am not sure, but perhaps that is about their respective national capitalists competing or simply about territorial or other geopolitical disputes, in the context of an imperialist world. But I don't see why socialist states would not compete over resources and markets. Production and trade would still be important maybe even more important because it is directly being using for the people's welfare. I think this is true whether the socialist economy consists of worker cooperatives or public sector industries. People will be more motivated to fight over resources. I also don't see how changing productive relations ends geopolitical competition or the animosity between nations.