What event occurred in ireland that led to the mass immigration of irish people to the united states?

There was a potato blight which caused potatoes to become diseased. The vegetable was one of the most used over in Ireland and the peasant class ate it most because it was inexpensive. They also came to the United States because the US government offered free land out west for people to farm. Finally, they came over because it was easy to find work. One of the most famous events the Irish immigrants participated in was the building of the Erie Canal.
    

The answer is an appellate court.