It's more cultural colonization than syncretism. For example, America was culturally colonized by forcibly converting its inhabitants to Catholicism. Their temples were destroyed, the stones used to build churches, and while celebrations were still observed, the deities were replaced with Catholic ones. Even the folklore was rewritten with Catholic characters.

It wasn't syncretism, it was systematic eradication. Syncretism is more akin to reconciliation of different views.

Another appropriate word for the colonization of America is genocide.

I'm old enough to remember being taught how America was settled by expanding into the vast wilderness of the continent, and that sometimes they had skirmishes with natives but they found them new places to live.

It turns out it wasn't quite as neat and tidy as suggested.