The Tennis Court Oath was taken because of the rising discontentment of the Third Estate in France. People believed King Louis XVI was unprepared and unfit to deal with the problems his grandfather left behind. Therefore they resorted to try forming their own constitution, calling themselves the National Assembly. Representatives of the Third Estate came together at Jeu de Paume, an indoor tennis court, where they discussed the reforms proposed by John Necker, their Prime Minister at that time. Some reforms were that all citizens are born free with equal rights, all have a right to participate in electing representatives to make laws, all are entitled to free speech as long as it was not abused, and taxation will be related to wealth. The Third Estate was supposed to meet in Menus Plaisirs but they found the King locked them out, so they met at a nearby tennis court instead. There, they vowed to keep meeting in this tennis court until a new constitution for France was made. The Tennis Court Oath was an affirmation of the sovereignty of the Third Estate; it was actually the first time the Third Estate revolted against authority and because of their revolt they became united.
http://library.thinkquest.org/C006257/revolution/tennis_court_oath.shtml
http://www.bl.uk/learning/histcitizen/21cc/utopia/revolution1/tennis1/tennis.html
http://www.history.com/this-day-in-history/third-estate-makes-tennis-court-oath
Image: http://blogs.isb.bj.edu.cn
http://library.thinkquest.org/C006257/revolution/tennis_court_oath.shtml
http://www.bl.uk/learning/histcitizen/21cc/utopia/revolution1/tennis1/tennis.html
http://www.history.com/this-day-in-history/third-estate-makes-tennis-court-oath
Image: http://blogs.isb.bj.edu.cn