What is a key event related to the voluntary migration in America and what is its impact on history?

One key historical event that led to the migration of American citizens was the discovery of Gold at Sutter's Mill in California in 1848.  At first, this was supposed to be kept secret, but Sutter's workers spread the news and suddenly people from all over the world came to take advantage of the California Gold Rush.  Indigenous tribes suffered, as the new settlers took the land of the hunter-gatherers of the region.  Cities such as San Francisco sprang up overnight.  Some people made their riches in the goldfields, while others made a living from selling things to the miners, many of whom were single men with few domestic skills.  The California Gold Rush marked the first rush of Asian immigration to the United States--this sparked a wave of xenophobia which would end with the Chinese Exclusion Act in 1882.  California became a state without having to go through the territorial process--its admission as a free state temporarily broke the balance of power between free states and slave states in Congress and necessitated the Compromise of 1850.