Simplify the following text for a Grade 6 native English-speaking person.
Original: Prussian troops played a key part in the victories of the allies in 1813 and 1814 , and the King himself traveled with the main army of Prince Schwarzenberg , along with Alexander of Russia and Francis of Austria .
Simplified: Prussian troops played a key part in the victories of the allies in 1813 and 1814 .