Because they didn’t want to put there citizens in a war
Answer:
In April 2016, Chinese Railroad Workers Project scholars from Canada, China, Taiwan, and the U.S. traveled to the Sierra Nevada mountains to explore tunnels — many of them cut from solid granite — that Chinese workers excavated.
The terrain was unforgiving, even in the spring. Fisher told The New York Times that the guide she and her colleagues had been traveling with slipped on a patch of black ice in a tunnel and broke their shoulder.
“We literally would not be sitting in these buildings — these buildings would not exist — without the work of these Chinese workers.”
Shelley Fisher Fishkin
The labor was undoubtedly dangerous. Chang said that great numbers died, perhaps over 1000 workers. Construction casualty records were not kept, so the specific number remains unknown, but historians estimate that one in 10 workers lost their life from explosion accidents, landslides, avalanches, heatstroke or hypothermia. Research also shows the callous way in which Chinese workers, whose individual names were not recorded by Central Pacific, were often treated.
“To avoid interrupting construction schedules, labor contractors and line supervisors maintained a pool of able-bodied men who could replace injured and dead workers at a moment’s notice,”
I would say that this can be seen in two ways:
a struggle of two world views: capitalism vs communism
or
a struggle of two superpowers to have control over the other countries: the US and the Soviet Union (as it can be argued that the two countries were not satisfied that other countries had the same system as they, they also sought control over them).
