What do child labor, railroad strikes, socialism, and the rise of labor unions all have in common

They all share in common that each involves unfair amounts of labor for people. Socialism involves manual labor; child labor is non stop work for young and hungry kids; Et Cetera. Not only that, but in almost all of them the people being forced to work were treated poorly.

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the mongolian invasion of china and central asia resulted in a disruption of the silk road as the chinese garrisons lost support from the chinese kingdoms which fell under the mongols. however, as the mongols established a formal dynasty in china, the successors of genghis khan restored the garrisons along the silk road allowing the safe travel caravans again.

the answer is a) to be able to obey them.