What historical developments presented new opportunities for women in society from 1865-Present?
You have a 145 year time frame, which is a huge amount of time and history when dealing with a general topic like advancements for women, so let me try to cover a few of what I believe are the most significant developments and opportunities were over that time frame. Keep in mind it will be nothing like a complete list.
From 1865 - 1900, a time period called the Gilded Age in American History, women entered the industrial work force in large numbers. While pay was very low and working conditions difficult, accessing the workplace led to greater opportunities and economic power for women later on.
In 1917, America entered World War I, and millions of white men went into the armed forces and overseas, leaving a dire need for workers in arms industries. These jobs were often filled by women, who tended to be, believe it or not, more sober than men. Women led the Temperance movement during this time, and their involvement in both of these developments led directly to the passage of the 19th Amendment, giving women the power to vote.
In 1960, the first reliable birth control pill was invented, giving women, for the first time ever, a way to plan the size of their families. This allowed women to become more educated, to pursue careers and to assume a role in society that had long been denied to them by their mere biology and longstanding gender roles.
The invention of the telephone and typewriter must have added two new careers for women. It added phone operator and secretary to teacher, nurse, and ... well we need not mention the other one.
The need for women computers during World War II must have added computer programmer to the list.
I know that the term, woman computer, sounds like bad grammar because computers today are not people; they are machines. Before the war, computers were people. That means that when complex equations needed solutions, rooms full of people did the calculations on mechanical adding machines.
This is a bit off the subject but in the movie, Bridge on the River Kwai, one of the commandos that destroy the bridge is a human computer.
During the war the men were in the military, and women were hired to do the calculating. The volume of calculations led to the building of faster caculating machines, which needed to be programmed. Some of the women computers became computer programmers after the war.
As a previous poster mentioned, the wars led to women working in traditional male jobs. The process took decades. For example women were allowed to be telephone operators, but were not allowed work in switching stations. The phone company maintained that women could not lift heavy objects. The woman who filed suit to overturn the rule carried her two children into court on the day she testified. She must have impressed the jury (or maybe judge) because she won. I don't have a footnote for that, but I think that case happened sometime in the 60's.