Butchering the definition, imperialism is the monopolist stage of capitalism, specifically the monopoly of finance capital. This can be expanded but there is no point in doing so here.

The monopoly on finance capital is already formed by a cartel of mostly american+european financial institutions and so on. These countries are what we call imperialist, we do not call Russia imperialist simply because they do not have this monopoly and are actively fighting against it, their future ambitions are a story for another day.

Let's say that somehow the cartel completely disappeared and banks were to start from zero again, a bunch of local banks would emerge all around the world. As time went on, the most efficient banks would inevitably best its competitors, consolidate their position and gain increasingly more market share, until it becomes a local monopoly, then they go global and the process repeats until a global monopoly is formed, this is what happens on every single industry.

This is an inevitable outcome of capitalism simply due the nature of capital growing, capital stagnates when it faces competition so capitalists inevitably organize into cartels to consolidate a monopoly. The only way to do some sort of "checked capitalism" is to completely strip capitalists off political power through a violent revolution, like China did.

When Cowbee says that capitalism decays and leads into imperialism this is what i think he means, and he is right.