Transforming is a practice of cutting flat areas out of it a hilly mountainous landscape in order to grow crops
The phrase "Join or die" means just that: Unless you decide to ally with them, they will outmatch and destroy you.
Hope that helped =)
I think the person that's being described is Henry Hudson. He took several trips out to sea and successfully made it to the New World on his third one. I think New York was also called New Amsterdam under the Dutch, but I'm not certain.
