Age of Empires II: Definitive Edition (PC) - Achievement - Scattered Horde
Kill all enemy commanders before defeating their hordes in "The Tatar Yoke".
This achievement triggers at the end of the mission. Start by taking Kiev (Blue) with your initial forces. You will encounter little resistance on the way there and in the city itself.
Once captured, you can begin producing units and upgrading, however you cannot buy new Villagers and must rely on supplies periodically from your ally, Kestutis (Teal). Supplies occasionally include new Villagers. You can also request specific supplies from your ally using the chat.
Part way through the level, an optional objective will appear to kill the leaders of the 3 x hordes. You must do this before destroying the hordes completely for the achievement to trigger.
Cannon Galleons may prove useful to snipe buildings (especially Castles) close to the shorelines.
You can lure the horde leaders away from their respective Castles and take them out with quick hit and run tactics. Each leader killed decreases the effectiveness of their horde.
If supplies run short, you can also destroy the enemy docks so that sea-trade can begin with your ally - A worthwhile endeavour given you can then use your limited Villagers to gather other resources than gold. Fishing Ships can also prove useful to boost your economy in the early going, given your limited Villagers.