Gate: Jieitai Kanochi nite, Kaku Tatakaeri, Seikaisuru Kado Recommendations
It's Basically a reversed version of gate.
Gate can be said to have three main parts to it: the military elements with the JSDF fighting in the Special Region, the "slice of life"/"fanservice" elements with Itami & others doing random things, and the "political" part about how Japanese and international politics deal with the existence of the Special Region. Seikaisuru Kado masterfully expands on that third part while (for the most part; the military plays a role, albeit a minor one) omitting the others: it shows how Japan and other countries react to a problem, or even an opportunity, that affects all of humanity, and makes some excellent commentary on the nature
Japan is met with an alternate reality, and the political war with the rest of the world ensues. An entity is given a lot of power of negotiation with the alternate world party.
That being said, Gate is pretty much a fan servicey fantasy-driven otaku pandering show with little substance, whereas Kado is about political negotiations about a sci-fi "what if" device and actually does make statements regarding humanity and philosophy of war, sharing and desires.