Because it was harder to travel over moountains.
The correct answer is a hypothesis
In the scientific method, a hypothesis can be defined as the provisional or attempted solution to a given problem. The level of truth attributed to such a hypothesis will depend on how the empirical data collected support or not what is stated in the hypothesis. This process, known as empirical contrasting of the hypothesis, can be carried out through confirmation (in the case of universal hypotheses) or verification (in the case of existential hypotheses).
1659 The Failure of the Commonwealth
1688 The Revolution
1707 The Act of Union
1807 The Slave Trade Act
1815 The Battle of Waterloo
1855 The Bessemer Process
1914 - 1918 The First World War
1939 - 1945 World War II
