Which battle stopped Italy colonising Ethiopia in 1896?

Adwa, on 1 March 1896, where an Ethiopian army under Menelik II destroyed an invading Italian force - the first time an African state had decisively beaten a European power in a set-piece battle, and one of very few times a colonial invasion was simply defeated rather than resisted.

It was not a fluke of terrain. Menelik had spent years buying modern rifles and artillery from several European suppliers playing against each other, unified a fractious set of regional rulers behind the campaign, and fielded around 100,000 men against roughly 17,000 - and the Italians attacked in fog on bad maps with their columns separated. Empress Taytu Betul, Menelik's wife, commanded a substantial force and had earlier cut the water supply to an Italian fort.

The consequences ran far beyond Ethiopia. It forced Italy to recognise Ethiopian independence, brought down the Italian government, and became a reference point for anti-colonial and pan-African movements for decades - and the humiliation was one of the things Mussolini explicitly invoked when Italy invaded again in 1935 with aircraft and mustard gas. That occupation lasted five years and Ethiopia counts it as an occupation rather than a colonisation.