Humanitarianism is the belief — and the work — that we should improve terrible living conditions and stop people being treated unfairly, especially when they cannot protect themselves. It is the -ism of humanitarian: the idea, not just the adjective. Red Cross work, refugee camps, campaigns against cruelty — these sit under this word. It is formal. You meet it in essays, news, and politics. People who like the idea use it with pride; people who distrust it say it can be naive, or that rich countries use humanitarianism to interfere. So the word names a real kindness, and also an argument about that kindness. It is simply humanitarian + -ism.