how did world war 1 influence european beliefs regarding imperialism?

Basically.. WW1 meant the beginning of the end for Europe. It would mark the beginning of European decline. No longer would Europe be the world's wealthiest and most prosperous continent. It would soon be superseded by the United States, and later on, Japan.

As such, imperialism, often reflecting prosperity and wealth, was starting to become unendurable. Desperately, European nations tried to hold on to their colonies, but after WW1, and certainly after WW2, imperialism was doomed. It was the American president Woodrow Wilson that said imperialism and any other form of colonialism was to be abolished.

In short: the destruction of Europe in the beginning of the 20th century gradually made imperialism unendurable. To this was added a growing sentiment of political incorrectness, due to American interference.

Hope this helps :)

It brought home to the European powers both how important is was to have an empire for strategic reasons and the cost of maintaining the empire.

It didn't do much. US president Wilson preached about it in his 14 points but the British and French ignored him, after all they had won the war, not the US.