From 1783 to 1853, the united states added new territory. 1. what was the significance of the louisiana purchase? 2. how did the united states extend its northern and southern boundaries? 3. what lands did the united states acquire as a result of the mexican-american war? 4. how did the idea of manifest destiny affect native americans? civil war breaks out between the north and south. 5. what issues caused conflict between the north and south? 6. what were the immediate causes of the u. s. civil war? 7. why did abraham lincoln issue the emancipation proclamation? 8. what were the long-term economic effects of the civil war?