What is a recurring event in the development of the united states? who were the first europeans to arrive in north america in the 15th century? between what two landforms did the louisiana purchase territory stretch? what negative effects were connected with the western expansion? what agricultural activities changed during the late 19th and 20th century? when was the us constitution adopted? 6.2 what was the average american’s job in the early days of the us? in what three areas is the us a world leader? where do the majority of americans have their ethnic roots? 6.3 why is the northeast referred to as the gateway to america? what is the midwest most known for? what geographical factors make the midwest a center for trade? what is a common nickname for the south?