Why did the us government establish washington territory in 1853?

In this period of time, there were demands from a sector of society(settlers in the northern part, beyond the Columbia River) for a self-government territory due to the fact that this was a place with lots of farmers and new-comers.  

After a series of civic, military and other confrontations a convention was formed to ask for a territory of their own, arguing several needs, but one common concern was how distant this land was from the capital of the Oregon Territory. It was then approved by the local Oregon government and then by the federal government.

In short, due to all these reasons, the cause can be said to be the need for self-government in a crowding area of settlers northern from the Columbia River.

a woodchuck would chuck 12.5 wood : 3