For the Seven Years War, I suggest: 
The Battle of Kolín on 18 June 1757 saw 54,000 Austrians under Count von Daun defeat 34,000 [color=7ea7d8][b]Prussians[/b][/color] under Frederick the Great during the Third Silesian War. We would take on a role in the Prussian Army under Frederick the Great.

In the Napoleonic Wars, I suggest:
The Battle of Leipzig fought from 16 - 19 October 1813 saw 195,000 soldiers under the command of [color=7ea7d8][b]French[/b][/color] Emperor Napoleon Bonaparte lose to a coalition force of 365,000 men from Russia, Prussia, Austria, Sweden, Mecklenburg-Schwerin, Saxony, Württemberg & the United Kingdom.

For the Great War, I suggest:
The Battle of the Somme fought from 1 July 1916 to 18 November 1916  with Over 3,000,000 soldiers participating and over a million combined casualties on both sides. This was probably the deadliest campaign in the history of human warfare with the British and French Armies losing 620,000 and the Germans losing 440,000 men.

Regarding WWII, I have read extensively on many accounts of various battlefields around the world. I know I can come up with something, but I will leave it up to you.

For Vietnam, I would like to go with units of the 173rd Airborne in the Central Highlands in 1967.

For GWOT, if we get that far, I know I can come up with something.

I may just delete the War with Spain in 1898.