He vetoed it for various reasons. For starters, he believed that it was a thing up to individual states and that it infringed on the states right to choose. Another reason was that he believed that such beneficial extension would not make people equal, but rather it would be racist towards the white people. His main argument, however, was that the bill would have a certain group gain rights that they are not entitled to, while a large part of the states does not even have representation in the congress, and that the congress needs to be enlarged first.
Due to Union measures such as the Confiscation Acts and Emancipation Proclamation in 1863
On May 10, 1869, at Promontory Point, Utah, workers drove a spike that linked two rail lines, one snaking from the East, the other from California, completing America's first transcontinental railroad. This event helped launch an era of economic development that would transform a Jeffersonian society of yeoman farmers into an industrial powerhouse.
Mhmm interesting question