Shirogane no Ishi: Argevollen

Both of these anime have mecha in in but that is not the main focus. You wont see huge battles that last 20 minutes or finale battle where the mecha fight to the death. It is way more of story line driven the people seem more real like you see in real life. These don't glorify war and focuses on the metal aspect of these characters, if you want high pace fighting this not for you. 

If Mobile Suit Gundam is "Military Unit Fights to Survive With the Help of a Big White Robot Amidst a War Stalemate in Space," then Shirogane no Ishi: Argevollen is "Military Unit Fights to Survive With the Help of a Big White Robot Amidst a War Stalemate on Earth." (Although I suppose Argevollen might actually be silver considering the title of the show, but I digress.) I personally think both shows strike a good balance between mecha action and the struggles of war both on the battlefield and behind the scenes in the government quite well. Alongside this, the dynamic between the protagonist and one of the antagonists is quite similar (Amuro and Char from Gundam and Tokimune and Richthofen from Argevollen) where a rookie pilot who is thrust the responsibility of using a state-of-the-art mech clashes with an ace pilot from the opposing military whose experience surpasses the need to rely on a machine with the best current technology. read more 

War between two countries. Main characters are part of military squads. Their squads accomplished many impossible missions and and earned great reputation. Also both squads have very powerful secret weapon (robot in Shirogane no Ishi: Argevollen and tank in Senjou no Valkyria: Gallian Chronicles). However time is different. Shirogane no Ishi: Argevollen is in future (not so far from nowadays, their just have primitive robots) and Senjou no Valkyria: Gallian Chronicles is in past, about WW I.  

> Both are about mechas > The MC in both have a special mecha,that can take over the enemies > Both have nations that fight one against the others with the mechas( Athens and Krishina in Broken Blade/Arandas and Ingelmia in Shirogane no Ishi) > Both talk about political aspects and make a reflection about the life 

both about mecha's both about people in war rinne no lagrange is about three girls and also has fighting planets. 

TACTICAL REALISTIC MILITARY ACTION That words tell everything about both anime Alot different between both anime so i will only tell you the similar thing only : + MC (always) fighting in group not alone, just like real soldier in battlefield + Instead using super weapon or power, MC & his allies using strategy to take down the enemies + Character Development is steady, so you will never see one or two character become super-duper-like-god in just one episode  

Both anime is centered about a division/squad of mechs in an ongoing war. It's coincident that both divisions share same number - 8.