He will take your sons
1 Samuel 8:11 And he said, This will be the manner of the king that shall reign over you: He will take your sons, and appoint [them] for himself, for his chariots, and [to be] his horsemen; and [some] shall run before his chariots.
http://www.law.cornell.edu/uscode/html/uscode50a/usc_sec_50a_00000453----000-.html
TITLE 50, APPENDIX App. > MILITARY > ACT > § 453
§ 453. Registration
How Current is This?
(a) Except as otherwise provided in this title [sections 451 to 471a of this Appendix] it shall be the duty of every male citizen of the United States, and every other male person residing in the United States, who, on the day or days fixed for the first or any subsequent registration, is between the ages of eighteen and twenty-six, to present himself for and submit to registration at such time or times and place or places, and in such manner, as shall be determined by proclamation of the President and by rules and regulations prescribed hereunder. The provisions of this section shall not be applicable to any alien lawfully admitted to the United States as a nonimmigrant under section 101(a)(15) of the Immigration and Nationality Act, as amended (66 Stat. 163; 8 U.S.C. 1101), for so long as he continues to maintain a lawful nonimmigrant status in the United States.
(b) Regulations prescribed pursuant to subsection (a) may require that persons presenting themselves for and submitting to registration under this section provide, as part of such registration, such identifying information (including date of birth, address, and social security account number) as such regulations may prescribe.
http://www.sss.gov/PDFs/32_CFR.pdf
http://en.wikipedia.org/wiki/Selective_Draft_Law_Cases
http://www.sss.gov/fspostdefer.htm
https://www.sss.gov/sssyou/sssyou.htm#Who%20Is%20Exempt%20From%20Registration?