It was not until the latter half of the twentieth century that trousers for women actually became a fashion trend. Prior to that, trousers were just worn by women (of course the trousers that the fair sex wore were carefully altered to suit the difference in figure) for the prospect of outdoor work.
In addition, it was not a recent development. For about hundred years, women have been wearing men’s trousers. They have continued to do so until the late twentieth century when trousers actually became a fashion statement for the fair sex.
Around the middle of the nineteenth century that in the Victorian society by the Wigan pit brow girls who used to work at the local coalmines, for ease in the course of their task, started wearing trousers. It was something that left the entire Victorian city scandalised. These girls were one of the pioneers who were actually responsible for starting the trend (even though it was not a fashion trend, it still classified as a trend that was unknown to the society and the world) of wearing trousers.
Although they wore skirts over their trousers, they rolled them up to the waist in order to keep the long flowing skirts out of the way. Even though the pit brow girls worked on a level above the ground at the pithead, the entire task of sorting and shovelling coal was definitely a labour that was hard and demanding in nature, wearing skirts must be a hindrance for whosoever wore it.
This move encouraged many in other parts of the world as well. For example, women working in the ranches in the United States (it was still the continuity of the nineteenth century) also chose to wear trousers for the prospect of riding. Later on in the early part of the twentieth century, aviatresses and other kinds of working women also followed suit and started wearing trousers.
The trend went one-step further when some notable female celebrities such as Marlene Dietrich and Katharine Hepburn had pictures taken of them wearing trousers in the era of the 1930s, a trend that was encouraged further by them, as they played a role in making the prospect of wearing trousers easier and less controversial for women.
Then came the second World War and women working in factories and being involved in work that was most particularly meant for men (in attribution to its hard and demanding nature) on the war front demanded the empowerment of wearing trousers. Even when the war had ended, trousers for women gradually found a level of acceptance in the general society. For instance, there were tasks like gardening or enjoying at the beach and other kinds of leisure pursuits, the entirety of which was made lighter for women once them wearing trousers was not viewed with disapproval.
Overall, the trend for wearing trousers in women had a very gradual process of gaining acceptance. Nevertheless, it did happen to garner public support and make lives easier for women who wore them.