Benjamin Franklin, publisher, diplomat, framer of the Declaration of Independence and the US Constitution, inventor of the lightning rod...the Franklin stove and bi-focal glasses, also adapted and made popular "gallowses" or suspenders around 1736 He made them part of the uniform of the nations first volunteer fire department in Philadelphia. "Why do firemen wear red suspenders?", the inspiration for gallowses probably came from gallows, which is a method of hanging things.
The first gallowses had a H back, and then, in the 18th century they crossed over in a X back. Finally in 1850, they finished in a Y back which is still around today.
The first patent ever issued for modern suspenders (the kind with the familiar metal clasp) was issued to an inventor called David Roth (US patent # 527887 issued in October, 1894. On December 19, 1871, Samuel Clemens or Mark Twain received the first of three patents for suspenders. Twain is the famous American writer and the author of Huckleberry Fin.
Original braces were first made of silk or satin and fastened to trousers with buttons. They were also very ornate.often embroidered by a sweetheart. Debussy's braces were floral patterned. Napoleons had a bee insignia. Queen Victoria gave Disraeli a pair embellished with fox hunting scenes. Franklin D Roosevelt had a pair bearing flags and eagles.
The hot summer of 1893 drove men to give up their braces and opt for belts.The trend continued and the popularity and acceptability of belts increased. At the beginning of the 20th century, very few dress trousers were made with belt loops. Today few are made without them.
A point to note is that the site at http://www.ushist.com, the U.S history clothing suppliers, states that "belt loops were not added to civilian mens trousers until the 1920's". The type of pant stated on there was the style from 1858-1889. From the 1890's on they were the peg top style...meaning that the legs were tapered from the crotch to the ankle, button fly, side seam front pockets and a single back with a right hip pocket as standard.