Under US Martial Law can the government force a citizen to become a soldier in an emergency
What does your common sense tell you?
Forget the law, think about your question.
You KNOW the answer.
Here are a couple hints.
President Sam Houston declared martial law in the Republic of Texas in 1842, when a Mexican column invaded and briefly occupied San Antonio.
In 1844, Joseph Smith declared martial law in Nauvoo to protect himself from criminal charges.
Finally, declaring martial law in the USA is akin to teaching a cat to speak, read, and write in Latin, French, German. Greek, and English; all the while wearing a three piece suit and standing upright the way primates do.
US denizens are a contrary lot by nature and ancestry.
Look back to the Vietnam war era, where thousands of people refused to allow themselves to be conscripted, fleeing as far away as Sweden to avoid Uncle Sammy's long arms.