Geography and circumstance.

I'd recommend reading Why the West Rules - For Now by Ian Morris. The book is controversial and definitely not the last word, but is worthwhile for its grappling with the big picture.

Relevant to your question, Morris makes the case that there was economic pressure on Europeans to sail west. Everybody wanted silk and spices from India and China. For Europeans, this meant trading with Arab, Iranian, and Turkish merchants, and so spices were expensive. Finding direct routes to China and India meant people would be able to buy silk and spices more cheaply, which would make people rich. So lots of people were very interested in sailing all the way around Africa, or going west to get to the East.

Hence Columbus stumbling onto the Americas. And then colonialism happened.

But this isn't a uniquely European thing. When Columbus arrived, the Quechua were already doing very European-style colonialism, and the Aztecs had a form on imperialism quite similar to the ancient Greeks. Carthage, Greece, Iran, and tge Arabs all engaged in imperialism and colonialism, but the European powers won.

Which, to be clear, doesn't mean it's right for anybody to do it.