Read the preamble of the 1842 Choctaw Constitution. Then answer the questions that follow.

We, the people of the Choctaw Nation, having a right to establish our own form of Government, not inconsistent with the Constitution, Treaties and Laws of the United States: by our Representatives, assembled in Convention at Nanihwaiya on Thursday the tenth day of November, 1842, in order to establish Justice, insure Tranquility, promote the general Welfare, and secure to ourselves and our Posterity the right of Life, Liberty and Property: We mutually agree with each other to form for ourselves a free and independent Government.

And we do hereby recognize the boundaries assigned the Choctaw Nation by the second article of the treaty made and concluded with the United States of America at Dancing Rabbit Creek on the 27th day of September 1830: viz. beginning near Fort Smith where the Arkansas boundary crosses the Arkansas River, running thence to the source of the Canadian Fork, if in the limits of the United States, or to those limits, thence due South to Red River, thence down Red River to the western boundary of the State of Arkansas, thence North along that line to the beginning: the boundary of the same to be agreeable to the Treaty made and concluded at Washington City in the year 1825.

Part A
What is the main purpose of the preamble of the 1842 Choctaw Constitution?