Which group of workers filled labor shortages to build the transcontinental railroad before the end of the civil war?

Which group of workers filled labor shortages to build the transcontinental railroad before the end of the Civil War?

Explanation:

The rail line was built by three private companies on public lands provided by extensive land grants from the United States.

Most of the semi-skilled workers in the Union Pacific were recruited from the many soldiers unloaded the Union and Confederate armies along with Irish emigrants.

The Central Pacific in 1864 hired some British and Canadian engineers and experts with extensive experience in railroad construction, but had a difficult time finding semi-skilled labor. Because of this, the railway experienced by local hiring Chinese emigrants as workers.