This is quite an unusual topic, I think, but an interesting one. Some speeches that I can think of are ones which try to inspire those who are going into battle. Some of these include Winston Churchill's speech following the fall of France in 1940 which ends "this was their finest hour". Churchill was the British Prime Minister, whose aim in this radio broadcast was to calm the fears of his countrymen and unite them in patriotism. There is a famous speech in Henry V by William Shakespeare, Act 3.i, beginning "Once more into the breach" as the men prepare to fight and another in Richard 11, starting "This royal throne of kings" which specifically mentions that they are fighting for 'Christian service and true chivalry." (Shakespeare again). Abraham Lincoln's speech, often called The Gettysburg Address' is very famous and easy to find. This American president speaks emotively about the idea that 'this nation, under God will have a new birth of freedom' because of the fight for a future, just, America in the civil war.
Some patriotic poetry, like "The Soldier' by Rupert Brooke about the honour of fighting for England in World War 1 are positive about battling for king and country-very sad, as he only lived for a few months of the war. Another poem which honours those who fought bravely is "The Charge of the Light Brigade" by Tennyson in the 19th century. There are also other poems and songs, like Red Gum's "I was only 19", Donovan's "Universal Soldier" from the 1960's and Wilfred Owen's "Disabled" and "Mental Cases" which are very bitter about fighting in a war to please those in authority and the terrible consequences that this brought for individuals and groups. So to a certain extent, it depends on whether you are looking for a genuine call to arms
or a parody or satire of the idea of "For King and Country." There are also many war posters from World Wars 1 and 2 which are a mix of written and visual patriotic propaganda. There are really quite a few texts around, but I'll stop there. Hope this is some help.
