Novel GATE: And Thus The UNDF Fought There V2

Decades after an alien invasion ravages the Earth, a mysterious portal opens in Iceland. When an army straight out of a fantasy novel comes through and slaughters all in their path, the nations of Earth are once more forced into a war they didn't want. Now for the first time in its history, the United Nations Defence Force is called to arms to defeat another alien force that has invaded the Earth, and are charged with spearheading en expeditionary force into the world they come from, and neutralize them once and for all!