I think I've bought nearly all of their history games on steam. Victoria 2 is great if you want a unique military/economic strategy game that focuses on 1840 to 1920. When I get bored of playing one of the larger players in imperialism, I delve into the "what ifs" and play as a more minor 19th century power like Italy, The Ottomans or China. Arguably, I had more fun bringing Japan into the industrial era than I did colonizing Africa with the UK. Also, uniting Germany is also quite fun. Plenty of great user mods out for it as well.
If you have an interest in 1920 to 1950, hearts of iron 3 is great. You can even import your end game from Victoria to it and continue playing an alternative reality 20th century.
Galactic Civ is turn based while Victoria and Hearts of Iron are continuous time, where you can speed up or slow down (or pause) time. It's a little weird at first if you're used to turn based, but the game flows much better as there aren't 5 minute pauses in gameplay unlike civ5.
It is a 4x in space not exactly the same as civ / ac, but it is very generic yet complete, similar to what civ 4 + beyond the sword is in its branch, and the general idea is the same: you start with a base planet (city), you have to expand your area to more planets (cities) all the while dealing with diplomacy and wars against several opponents ranging from nice and friendly to war mongering slavers.
And if you end up liking the genre, there are a lot of other 4x available with specialization in each specific area (sword of the stars, endless space, ai wars, sins of a solar empire, stardrive, star ruler, ...)
PS: and if you have never tried it, the mod Rise of Mankind + A new dawn breath a lot of new life to Civ 4 beyond the storm. The extent to which it deepens the game is unbelievable.