Complex sentence: In the 1780s the national government was able to settle the issue of the western territories, which were ceded by the states to Congress and became territories; with the migration of settlers to the Northwest, soon they became states.
Split into simpler sentences: In the 1780s the national government was able to settle the issue of the western territories, which were ceded by the states to Congress and became territories. With the migration of settlers to the Northwest, soon they became states.