Check the Spiral Wars series. This setting starts out as humanity ends their first great intergalactic war as the newest member of the space faring spiral community. A conflict that nearly wiped us out.

The series focuses on the capital battle ship Phoenix as it is used as a scapegoat for a navy coup. The first novel mostly focuses on Phoenix and it's officers as the ship goes on the run from humanity's own navy. The subsequent novels chart Phoenix journey far beyond human space as it slowly uncovers a threat to the entire spiral galaxy.

The two main characters are the captain of the ship and the major who commands the ship's power armoured marine corps that is used for boarding and ground actions.

The whole series is very militaristic as Phoenix makes allies and enemies in its quest to uncover the threat and find a way to fight it. There's a ton of space battles that focus heavily on the complexities of ship to ship warfare while the marine company provides plenty of hard as nails up close action, both in and out of their power armour.