From Halopedia, the Halo wiki
In Halo Wars, Deathmatch is a spin on regular skirmish where everything including all infantry, vehicle and air units, heroes and technologies start off fully upgraded: however, Leader Powers will automatically improve over time, though at a relatively fast pace. The player starts with 15,000 Supplies and all technologies are researched. The population total for all players starts at 15 and increases by 10 for each base that is claimed. Population, however, cannot exceed 99, so, if capturing bases once this cap is reached will not yield additional benefit. Like Skirmish, the game ends when all enemy bases are destroyed.
Halo Wars 2
Deathmatch returns in Halo Wars 2 as the default multiplayer gametype, in principle acting as a renamed Skirmish. In this mode, players start with 600 Supply and 400 Power, and must construct units and upgrade technologies manually. The game ends when all enemy bases are destroyed.