After the British took over the then New Amsterdam in 1664 and renamed it to New York, they took away the privileges that certain people in society had enjoyed such as women and black people.
In the case of black people, they removed many of them from the skilled jobs that they had and made slavery legal a year after they arrived. Some decades later in 1712 they clamped down even harder on enslaved people and limited their movements in the city and even sometimes refused white people from releasing them.
They brought horses. It was easier for them to catch up with the buffalo and hunt instead of having to throw weapons from a far and run after the Buffalo.
James Polk became president in 1845 with plans to expand American territory. His actions included the annexation of Texas and obtaining the Oregon Territory.