Our historical narratives reflect how we think about the reasons for colonial annexations. Colonial empires did in fact often use some concrete pretext (a raid with European victims, piracy, a treaty violation, a trade conflict, picking one of the sides in a civil or succession war, etc) to decide to annex countries. Certainly if the area annexed was one that other colonial powers had economic interests in as well, or just generally to justify the cost of going to war to taxpayers. But we typically take those pretexts about as seriously as Hitler's story that Poland started it in 1939, and ignore them when summarizing colonial history.

The inability of nations of "uncivilized natives" to honour treaties, protect traveling Europeans within their borders, or keep their citizens from raiding over the agreed borders, immediately disqualified their existence in the eyes of Europeans.