Complex sentence: His first experience of war came in November 1895, when he was attached as an observer of guerrilla warfare to the Spanish Army during the Cuban War of Independence, together with his fellow 4th Hussars officer, a twenty-one year old Winston Churchill.
Split into simpler sentences: His first experience of war came in November 1895, when he was attached as an observer, of guerrilla warfare, to the Spanish Army during the Cuban War of Independence. Together with his fellow 4th Hussars officer, a twenty-one year old Winston Churchill.