What is the importance of the Act of Union in 1841?

Do you mean the Preemption Act of
1841? If so, this law, also known as the Distributive Preemption Act,
allowed the sale of public lands at very low prices. It gave the right to squatters,
living on government land for at least 14 months, to purchase up to 160 acres for as
little as $1.25 per acre. Present territories that would eventually become states--such
as Alabama, Arkansas, Illinois, Indiana, Louisiana, Michigan, Mississippi, Missouri
and Ohio--would receive 10% of the total sales upon admittance to the Union. It was
particularly popular in the territories of Nebraska and Kansas, though claims were
greatly reduced after the enaction of the Homestead Act of 1862. The Preemption Act was
repealed in 1891. It served to greatly enhance America's dream of manifest destiny
during the 19th century.