Complex sentence: Casement, Figgis and Erskine Childers visited the London agent of a Belgian arms dealer, eventually closing with a dealer in Hamburg, introduced to them by O'Rahilly, who arranged the sale of 1,500 rifles.
Split into simpler sentences: Casement, Figgis and Erskine Childers visited the London agent of a Belgian arms dealer. They eventually closed with a dealer in Hamburg, introduced to them by O'Rahilly, and settled on a sale of 1,500 rifles.