Islam is a peaceful religion, then why has the Saudi Arabian flag got a sword on it?

See link; a href="http://www.google.co.uk/images?client=firefox-a&rls=org.mozilla:en-GB:official&channel=s&hl=en&q=saudi+arabi+flag&um=1&ie=UTF-8&source=univ&ei=ho8TTMOdIIaSuAeV9OSICg&sa=X&oi=image_result_group&ct=title&resnum=1&ved=0CCQQsAQwAA" rel="nofollow"http://www.google.co.uk/images?client=fi…/a