The Franco-Prussian war

The Franco-Prussian war (1870-1871) was a conflict between the kingdom of Prussia and the second french empire. It was started by the prussians ambitions of a united german kingdom under prussia. the war started when Otto von Bismarck provoked france into declaring war on Prussia and it's allies, the french attacked first, attacking the city of saarbrücken, But the French had underestimated the speed of prussian mobilization, not knowing that prussia had secretly prepared for war for several years. Though they took heavy losses, the prussians retook saarbrücken. Following this the prussians achived several swift military victories as the prussian army had superior guns and tactics and had gained a lot of experience from a recent war with Austria, and though the french army did have better rifles, they were poorly led and outnumbered 2 to 1. 
After a culminating battle at sedan, France surrendered to the prussians and the Second french empire fell. 
Following this victory, the german states united and the German empire was formed and germany became one of the dominant powers in mainland europe until it's fall in the first world war.