Answer: the answer is d...
Explanation: brainliest?
It was primarily "<span>d. the vulnerability to invaders from the north", since the Mongol territory was rapidly expanding--making the Mongol warriors all the more powerful. </span>
In the late 7th century, the Native American population dropped drastically due to a <span>contagious disease.
</span><span> contagious </span>diseases can transmit from person to another easily.
However, Ancient Rome was to develop its own form of government that allowed the Romans to govern themselves. Citizens of Rome would gather at an assembly to elect their own officials.