1. What do you mean by “opportunity”? Weren’t the zionists the ones who created the opportunity? Why couldn’t that have been done previously? (It’s possible you are right and it couldn’t have been done – I am just wondering why.).
It was very difficult to move to Palestine before 1917. The Turks who controlled it allowed very few jews to move there and the ones who were able had trouble because it was difficult to make a parnassah there .
As a side not the Gedolim also forbid jews from going to america as well. They called it a Treif Medina and quote obvioulsy they changed their mind