As new states entered the Union, their senators would be assigned to two of the three classes.

It enters the Union as a free state in 1820.

By 1850 California entered the Union as a free state.

Some officials now suggest that all 10 states might not enter the Union at the same time.

California entered the Union in 1850 as a free state; the other areas would remain territories for many years.

Even after it entered the Union as the 14th state in 1791, relations were still uneasy.

Oregon entered the Union in 1859 as the 33rd state.

The pressure for more space intensified at the end of the 1880s, as six new states entered the Union.

Each new star on a flag is noted, along with the date that the state it represents entered the Union.

Arkansas became the 25th state to enter the Union in 1836.