Because. English examples, 15561682 (N.E.D.). Much used by children and illiterate people in the U.S.
1798. [He] said so to make fun of me, cause I was a Jarzyman.The Aurora (Phila.), Dec. 13.
1816. Cause youve got 20, or 30,000 dollars, you call it a glorious treaty.Mass. Spy, May 1.
1856. Do you eat johnny cake? cause if you dont Ill cut some wheat bread.Whitcher, The Widow Bedott Papers, No. 7.
1884. Harpers Magazine. (N.E.D.)