From
World Wide Words: Bulldozer:
The word is definitely American. The earliest sense had nothing to do with machinery, but referred to a severe punishment, in particular one applied with a bullwhip. Detailed explanations appear in several US newspapers in the latter months of 1876, the earliest I’ve found being the day before the presidential election of 1876, which historians suggest may have been the most hard-fought, corrupt and rigged election in the history of the Union. All say that it came into being as a result of a determined attempt by Democrat supporters in the Southern states to stop blacks from voting Republican. This is the way the origin of the expression was explained in the Gettysburg Compiler of 11 January 1877:
In very obstinate cases the brethren were in the habit of administering a “bull’s dose” of several hundred lashes on the bare back. When dealing with those who were hard to convert, active members would call out “give me the whip and let me give him a bull-dose.” From this it became easy to say “that fellow ought to be bull-dosed, or bull-dozed,” and soon bull-doze, bull-dozing and bull-dozers came to be slang words.
Several articles use bull-dozers for the individuals who were doing the intimidation, as in this item from the Janesville Gazette of Wisconsin in November 1876:
“Bull-dozers” mounted on the best horses in the state scoured the country in squads by night, threatening colored men, and warning them that if they attempted to vote the republican ticket they would be killed.
By the early 1880s, to bulldoze was to intimidate or coerce by violence, specifically the threat of a flogging. A bulldozer could be a bully, an intimidator, or a member of a vigilante mob. It could also refer to a type of gun, presumably seen as a usefully intimidating device.
The next step occurs around the end of the century. We start to get references to bulldozer being the name for various items of equipment. The earliest is for a machine in a blacksmith’s shop for bending big pieces of metal. There’s no way to tell whether this sense appeared independently or had been borrowed from the earlier ones, but the ideas are sufficiently similar to presume a link of some sort.
A bulldozer working on a rubbish dump.
It's been a long journey
from uncondign punishment
In 1910, a Pennsylvania news report said that a boat had been bought to scrape out and clean the channels of a canal, which came supplied with a bulldozer — from the description a device for mounting on the bows of the boat — to break up heavy ice in winter. Crude mule-powered earth-movers were also said to be fitted with such a bulldozer (the problem, it was said, was getting the mules to go backwards ready for the next stroke).
As you can imagine, in time bulldozer for the pusher device at the front of a machine became confused with that of the machine that did the pushing. But the first cases of bulldozer for a tractor fitted with one appear only at the end of the 1920s and are usually linked with the then new Caterpillar tractors. After that, of course, a retronym had to be invented to describe the item once called by that name, and bulldozer blade came into existence.
