Complex sentence: All the conference invitees brought Luciano envelopes full of cash to welcome him back from exile, which Lucky Luciano used to finance his interest in the Hotel Nacional and casino with Meyer Lansky.
Split into simpler sentences: All the conference invitees brought Luciano envelopes full of cash to welcome him back from exile. The money was used to finance Luciano's interest in the Hotel Nacional and casino with Meyer Lansky.