2Pac waz attacking him 4 things done off wax. 2pac took Biggie under his wing and let him perform at his shows. Biggie waz part of that Thug Live movement (not the group), but when 2pac went 2 jail, that all changed.
Biggie waz working with Bad Boy, Puffy changed his image (compare "Party And Bull$#!+" and Heavy D's "A Bunch of N!gg@z" to his Bad Boy stuff). He ditched 2Pac's Thug Live movement, then jacked the formula that Pac used on Me Against The World (talking about death and stuff he didn't have like money and girls). Biggie success put him on the same level that 2Pac waz at commercially but wazn't giving props 2 him.
On top of that, 2Pac believed that when he got shot and checked 4 his jewely in NY, that Biggie new about it and kept telling him 2 watch out but never told him when it waz going 2 happen.
Last year i watch a Biggie special on VH-1 and one of Biggie's friends or family said that when they met up backstage at an award show that Biggie stopped 2Pac (in the middle of all the beef) and waz like "what are you doing?" And 2Pac waz like "i gotta do what i gotta do, and this is getting us both more sales." I don't now if that's legit or not or a just a PR move.
Either way, there it is in a nut shell. There is one Biggie line that pokes fun at the beef. Since i'm not a Biggie fan, i don't know what song it is (one of my friends back in the day had it) where Biggie had a line that said something like "if Faith has kids / it's probably 2Pac's."