Complex sentence: In late 1945, mobster Bugsy Siegel and his "partners" came to Las Vegas, after the fledgling resort city piqued Siegel's interest due to its legalized gambling and its off-track betting.
Split into simpler sentences: In late 1945, mobster Bugsy Siegel and his "partners" came to Las Vegas. Vegas reportedly piqued Siegel and his mob's interest because of its legalized gambling and off-track betting.