...and I'm sure that Cuban guy ended up dead

Fred Weiss. The murder of Weiss, who was essentially a civilian brought immense heat. If Weiss had lived to testify (Gotti had suspicions) it would never have caused as much damage as there was after the murder. It's the reason Vinny Ocean and Anthony Capo (both NJ) flipped. It brought down the DeCavalcante family.

JCrusher, you have an interesting theory on DeMeo and Gotti. While I disagree for those reasons, Gambino soldiers have been heard lamenting DeMeo's death on wiretap, believing he was killed for nothing. In that sense I think you're right. Paul had the excuse of hitting DeMeo for breaking LCN law within the realm of earnings, but I think the family sensed it was more just 'because I can'. Nicky Scarfo's Salvie Testa hit (another good example) was the same thing. Technically he had motive when Salvie arrogantly broke off the wedding with Chuckie Merlino's daughter, but why wouldn't their respective families get nervous when powerhouse made men are knocked off just like that?

Joe Masseria didn't really think his murders through. He may not have realized how clannish the Castellammarese were or how they functioned as a sort of secret society that was practically built for banding together and surviving. Ordering the deaths of all of them whilst hitting his most influential lietenaunt, Gaetano Reina was certainly ill advised. Look how it came back to haunt him.

And murdering the Scalvo brothers sure didn't end well for young Billy McCarthy.