Not my genre but in case Woodie Guthrie and Pete Seeger haven't been mentioned already then they need to be (I guess they're more folk than country...)
Jesse Welles isn't necessarily tankie country but he's at least adjacent and he deserves a lot more attention.
Mon Rovรฎa is another contemporary folk/country artist that sings with anti-war and post-colonial lyrics, drawing on his personal experience in war torn Liberia and living as refugee.
There's also Kimya Dawson and her work (e.g. from the Moldy Peaches era), although that's mostly folk-punk revival so it's not something that is to the taste of all people who like pure country music. Another tankie-adjacent example while not necessarily being tankie.
