Parashot Matot - Masei | From Dependency to Independency

The last two Parashot of the book of Bamidbar describe the request of the tribes of Reuven and Gad not to enter the Land of Israel and to remain on the other side of the Jordan river and Moses's reaction is very harsh. Why is Moses angered by their request? Can we see a connection to the next Parsha (Parashat Masei) that describes the journeys of the people of Israel in the desert. Why is this list needed? What do these journeys teach us about the development and transformation that prepared the people of Israel for their entrance into the Land of Israel?