Warhammer doesn't have any diplomacy or unit creation mechanics. You start with an army of a certain size, and you can hold part of your army in reserve, but that's it. When they die, they're dead. Each of your little guys was also hand assembled and painted by you, and you might have invented backstory for your army and generals. For example, your WAAGH! could be the Rippin' Roughboyz, who prefer to get up close and personal with lots of melee units and giant mechs. Your WAAGHboss is the legendary Ironskin Thunka, an ork who has had so much of his body replaced with scrap metal prosthetics that some doubt there's even flesh beneath all that steel and slag.

Here's the most legendary and well-known game of Warhammer in wargaming history: https://imgur.com/a/cant-cheese-cheeser-warhammer-V0gND