The country faces a shortage of troops in the campaign against Russia's better equipped and larger military
The crowd chanted 'Oh Jeremy Corbyn' and waved flags with the Labour leader's name on as he came on stage, introduced by Glastonbury organiser Michael Eavis.
Addressing the crowd, Corbyn urged that there should be a more humane world, saying: "Build bridges not walls."
In a wide-ranging speech covering environmental issues as well as racism, Corbyn also spoke about the recent general election, saying he was proud of his party's campaign, which he said brought "a lot of people back into politics".
Corbyn was on the main stage at Glastonbury for about ten minutes before American hip hop group Run the Jewels performed.