1. SENTINEL WAS GOING TO KILL HIM ANYWAYS Doesnt anyone remember before the part where Megatron saves the day, Sentinel was going to use his sword thing to destroy Optimus? 2. SENTINEL KILLED ONE OF OPTIMUS'S FRIENDS 3. SENTINEL WAS GOING TO ENSLAVE THE HUMAN RACE Optimus was friends with many of the humans. He didnt want to enslave them. Earth was a fine home. 4. OPTIMUS WAS TIRED TO WAR He had been in this war for many years. Many many years. Despite the fact he is an absolulate killing machine, he doesnt like this war and just wants it over. Even if Megatron offered a truce, it was obvious Megatron was going to betray him sooner or later. 5. MEGATRON TRIED TO KILL PRIME BEFORE remember in the 1st and 2nd movies?