Complex sentence: When the soldier threatens to tie Quito to his horse, Sgt. Hook takes Quito onto his own horse, declaring that a boy just needs a firm hand, and slaps Quito across the rump, placing the child in front of him on his saddle.
Split into simpler sentences: When the soldier threatens to tie Quito to his horse, Sgt. Hook takes Quito onto his own horse, declaring that a boy just needs a firm hand. He slaps Quito across the rump, placing the child in front of him on his saddle.