1) Those that hold that it is tied to how we were treated look at the 3 Shvuos like the rules of Galus. If part is not kept, the other part falls away, as well. I personally would not subscribe to this opinion, but there were those that held this way, and I can not mock it.
2) The legal ruler of the land was the League of Nations (UN wasn’t invented yet) and that’s what counts. Rav Nachman in Eizehu Neshech had people work for him, against their will, because of the king’s law. I never heard of a Halacha that you must listen to every and any goy. You’re lucky no goy ever told you to jump in the lake — because, don’t forget, it is a Yehoreg v’Al Yaavor!
Besides, you are making a very big mistake by thinking that the land was full of Arabs before Jews came. Arabs came there because of the Jews, because of job opportunities. That is why they settled near Jewish towns.
3) Perhaps.