Pallets have been around for a long, long time. Believe it or not, Skids (another work for pallets) go back as the 1st millennium B.C. Even the Ancient Egyptians used pallets to store their various supplies and food stores.
In our society, the substantial use of pallets began with the development of the forklift. Back in Word War II, pallets were critical in the logistics operations. As forklifts were used more and more, the general design of the basic shipping pallet, or skid, had to change. There are several patents starting from 1929 that continue to 1949.
What is really interesting about the pallet is where the modern designs come from. As it turns out, most improvements and developments were made during the war to increase productivity. At this time, forklifts were widely being used for the first time and people were figuring out that there was a better and faster way to pick the skids up. From this concept, the 4 way pallet was created. An interesting fact is that the 4 way pallet was not actually patented until after the war in 1945 by a Navy Officer named Robert Braun.
If you want any more information on pallets, I would suggest reading up on them from a credible source. Check out Wikipedia for some quality information: