German gunboat SMS Iltis raises the German flag on Yap ahead of the Spanish ceremony.

What happened

The gunboat Iltis arrived on 25 August (early morning in Habele’s account, 5:20 pm in the Spanish Wikipedia), landed a party and raised the German flag before the Spanish could hold their ceremony. News of it set off riots and protests in Spain, and Bismarck proposed Pope Leo XIII as mediator. Some sources give other dates: MicSem’s list has 26 August, and English Wikipedia 2 August.

Why it matters

The flag dispute led to the papal settlement that gave Spain the Carolines and began Spanish colonial rule in the islands that now form the FSM.