Because trains started and people started working for trains.
A. Because the US for example is big and powerful because it has always been able to trade with different countries
To be protected, to get treated fairly, and money
The Mongols treated the non-muslim subjects most fairly, while the Ottomans treated them the least fairly.
The Mongols were religiously tolerant because they conquered and rule through manpower rather than religion. The Ottomans were the least fair to non-muslims. It is close between the Umayyads and the Ottomans, but the only difference is the amount of discrimination (per se) held against non-muslims. While the Umayyads only had the jizya (tax paid if you were non-muslim), the Ottomans had distinctive restrictions on non-muslims. They had dress codes according to their religion and could only reside in neighborhoods who's residents were of the same religion (under the Ottomans).