The 19th century was the 100 year time gap between the 18th Century and the 20th Century. Many important events happened in the 19th Century. In the United States of America there was the American Civil War when Abraham Lincoln and his armies defeated the slave owners of the south and freed the slaves. In Britain the Industrial Revolution continued and there were many wars.
According to Creationists, this is when the Earth was made. But for some unknown reason it was named the 19th century. Seriously even the silliest creationists know the Earth is at least several thousand years old. They're such cretins you can easily imagine they think the earth is only 2 centuries old.