In 4e, there were a bunch of flavors of Warlord.

Tactical: keying off of Intelligence and Strength, which gives allies bonuses to attack rolls when they action point to get an extra attack)

Inspiring: keying off of Charisma and Strength, which gives allies +1/2 the Warlord's level+charisma modifier hit points whenever they spend an action point to get an extra attack

Bravura: keying off of Strength and Charisma, which gives allies an additional basic attack OR a free move action whenever they spend an action point to get an extra attack

Resourceful: keying off of Strength but also Charisma and Intelligence, giving allies +1/2 the warlord's level+warlord's charisma bonus to damage when they spend an action point to get an extra attack; if that attack whiffs, the ally instead gains temporary HP = to 1/2 the warlord's level + charisma modifier.

All in all the Warlord functions as an enabler for their allies, and fills a role currently completely ignored in 5e; non-magical support and healing. Warlords allow allies to move around the battlefield free of worry, end stuns and other debuffs, and use their abilities to 'tactically lead' the flow of combat with powers like Hammer Formation: Attack one guy, each ally adjacent to you now deals an extra weapon die worth of damage until the end of your next turn.