The correct answer is the civilizing force of Christianity
Explanation: The Viking era came to an end due to the growth of Christianity and how Christianity entered society, leaving not much of the Viking culture left.
<span>Immigrants increase the threat of terrorism.
</span><span>Immigrants cause negative population growth. </span>
<span>The system of checks and balances works like this; when a bill is proposed the senate votes on it, if it passes there it then goes to the house of representatives if it passes there it goes on to the president who either approves it or vetos it. If it is vetoed or doesn't pass by two thirds in either the house or the senate it has to be revised and voted on all over again. If it makes it through all the checks then it becomes a law</span>
papermaking, gunpowder, compass.
