Prussia had a great martial tradition. Unfortunately in the early part of the Napoleonic Wars they were living on past glories and had a disastrous campaign in 1806. 

Still re-organising their army, they prevaricated too long to aid Austria in the 1809 campaign.

In 1812 the Prussians supplied a contingent to Napoleon to help guard the northern flank of the Grande Armee. During Napoleon's retreat from Moscow, the Prussian commander carefully separated his countrymen from the French troops with him and negotiated a settlement with the Russians. This eventually led to the Prussians declaring war on France and returning to the Allied cause for the 1813/1814 campaign.

1815. Beaten by the French at Ligny, two days later the British army would have been beaten at Waterloo without the Prussian persistence.

Most well known commander was Blucher. Hard fighting, hard drinking and thought he had an interesting relationship with an elephant. Nearly captured or killed on many occasions as he often led from the front. He was an inspirational commander.