Ok I've only watched part II completely once I've watched half of it a couple other times but heres what I didn't understand why did Roth try to kill Mike what would he gain from it?

Roth was behind the Rosato brothers who were in New York and with Michael gone Pentageli would of been weakened and it would of been easier to take over New York witout Micheal in the equation, thats what i think , am sure there will be various theories

Roth and Vito Corleone had been partners, but only in the Prohibition-era booze business, as Roth pointedly reminded Michael several times. But Michael had been greedily horning in on Roth's Western gambling empire even before Vito died. The first business deal we saw Michael involved in when he returned from Sicily was to push Moe Green, Roth's best friend, out of his Las Vegas hotel; later he had Moe killed because he resisted. By late 1958, when we first meet Hyman Roth, Michael has moved his entire operation to Lake Tahoe, owns three hotels in Nevada, and is about to force Meyer Klingman out of a fourth hotel, owned by Roth and the Lakeville Road Boys. And it's obvious that Michael has designs on Roth's Havana gaming empire. Small wonder Roth felt threatened, and concluded that the gambling business wasn't big enough for the two of them.

Do a search on this topic and you will find other interesting opinions.

Not to mention there was never any trust between Roth and the Corleones. Vito didn't trust him as Frankie pointed out and Michael certainly didn't ("He's been dying of the same heart attack for 30 years.")

Roth did think he would live for a long time, and he had no use for Michael horning in on his operation.

Thanks I get it now I was thinking of rewatching all three of them soon lol I found it easier to reread the book then to rewatch the movie which I found strange.

This also follows the pattern historically of American-Jewish organized crime figures moving into legitimate business - while the Italian CN fills in the gaps and dominates organized street crime.

There is a "Jewish Mafia" again - but it is made up of recent Russians and Ukrainians it has no connection to the prohibition era combines at all.