The Homestead Strike of 1892 occurred at the steel plant in Homestead, PA (near Pittsburgh) that was owned by Andrew Carnegie. The strike happened because the management of the plant, led by Henry Frick, wanted to break the union at the plant so that they could reduce wages more easily.
By this time in US history, labor unrest had become somewhat common. There had been the Haymarket Riots a few years before and a violent strike among miners in Idaho in 1892. The massive Pullman Strike was to happen in 1894. This was a time when businesses were growing larger and richer and management was trying hard to cut costs. It was also a time when unions were trying to gain power so they could demand better wages and working conditions for their members.
In the early 1890s, steel prices dropped dramatically. This led Frick to want to cut costs by decreasing the wages of his employees. Frick and the union were supposed to negotiate a new contract in 1892, but failed to come to an agreement. Frick responded by locking the workers out of parts of the factory. He then announced that he would no longer bargain with the union but only with individual workers. This caused the union to go on strike. The strike lasted five months and had episodes of violence, including an attempt to kill Frick. Eventually, the union lost and was broken.
So, we can say that this strike happened in Homestead, PA (outside of Pittsburgh) and that it happened because the steel company wanted to break the union so that it could lower wages and reduce the overall costs of production.