Pax romana is the answer to your question. It was period of prosperity for Rome
<span> The Germans called the US Marines The Hounds of Hell, We kept the nickname as Devildogs.
The Allies called us Doughboys either for are lack of Modern 20th Century Warfare, or the doughnut-shaped buttons on the uniforms.
Also we were called Yanks thanks to the song
"Over Their"
source: https://answers.yahoo.com/question/index?qid=20070409211306AAArT7q</span>
Answer:
They had to travel to find food
Explanation:
The development of the steam engine....of that is an option. You really should include the choices.