I have the perfect suggestion. Have you heard of Europa Universalis 4? It's on steam. It's a game, RTS style where in a given time in history you control a nation, and you manage diplomatic relations with other countries, either arranging royal marriages, alliances, and rivalries, and the main goal is of course to make your nation shine and be prosperous, so you may declare war on enemies and they may attack you too. Check some videos first if you're not convinced by what's I said. It's not that expensive either, though maybe it's a little over 30$ now, not sure at all. How you grow in this game (how you make your nation larger) is by conquering individual provinces either by demanding them in a war peace treaty or by annexing subject vassals. It's really well done, and with the mods… infinite possibilities. There's also a DLC to create your very own nation, which is extremely fun and creative.
If not, there's also Age of Empires II HD edition also on steam, also a RTS game but less complicated, you make troops, build stuff, attack enemies, collect resources, you get the idea.