Halo Wars 2 launched today, however, it doesn't have a competitive multiplayer ranking system. At least not at the moment. According to Eurogamer, 343 Industries and Creative Assembly said that the decision was made in order to first make sure that the game has the right balance in its gameplay.
Actually Halo Wars 2 does have a skill-based matchmaking system, but players can't see it as they're playing. This is of course unusual for a Halo game, since the series is known for its competitive community.
At the moment Halo Wars 2 shows Spartan Rank, which is tied to XP progression and not skill. This means that Spartan Rank is just an indication of how long a person has been playing the game.
One good guess is that a proper ranking system might eventually come in the form of an update or DLC. Is this an important thing to miss out, or can you live without it for the time being?