In an earlier post you said "The Mashiach- a king descended from King David- gathers in the exiles, fights the wars of Israel, enforces the Torah and rebuilds the Temple (=Beit HaMikdash)." I only wanted to clarify, does the Mashiach regather only the Jews or all the tribes? If He regathers all the tribes, how would this effect present day Israel?

All the tribes of Israel- Reuven, Shimon, Levi, Yehuda etc. are ALL JEWS. There are NO gentile tribes. The Mashiach gathers all of Israel, all the Jews, back to the Land of Israel.