Reincarnation Isekai Story : Finding More Isekai-ed People while transported by a Isekaied Myself !! The Battle of Isekai MC story Never Ends!!!

[Praybird]

There's a webtoon that's pretty much a war on Earth among teens who return from being isekai'd to different worlds.

And it's quite good.

The Warrior Returns

After saving one world, warrior Minsu Kim returns to Earth only to find that he’s lost everything... so he decides to destroy the world he used to call home. In his rampage, he kills teenager Jeongsu Park and his family. But instead of dying normally, Jeongsu is transported to another world...

m.webtoons.com