The drama of Downton Abbey begins when the Earl and Countess of Grantham's heir to their family estate (and eldest daughter Mary's marriage prospect) is killed in the sinking of the Titanic. Since Mary is one of three daughters, and the heir has to be male, the only way she can now inherit the estate is by marrying her cousin Matthew.
As was the case for powerless women in the Edwardian period, Mary is under an immense amount of pressure to get married to secure her position and fortune. In 1912, the marriage rate in the UK for women was twice what it is today. And at 20 years old at the start of the series, she's practically a spinster of the times, since she's already had several "seasons" to find a husband.
Mary isn't the only woman getting marginalized by the entail (unbreakable property inheritance agreement) of her family's estate. The only way Mary's father, the Earl of Grantham, was able to save the estate from financial ruin when he originally inherited it was by marrying a rich American heiress (Mary's mother). But even though it was the Countess's money that saved the estate, the rules of the times made it so that her daughters would get nothing after her death, and the fortune would instead go to a man — even if that's a distant male cousin.
Mary was set to marry a cousin she didn't even have feelings for in order to secure the family's fortune, and then after he died her next prospect was yet another cousin, Matthew.
While we find marrying relatives a taboo in the States, it's actually still legal to marry your first cousin in the UK (and the royal family has married cousins). And it was an especially popular way for big, wealthy families in the Victorian and Edwardian periods to keep wealth (and secrets) all in the family.
There's a funny scene in which Mary chides her father about sleeping in the same bed as her mom, and he responds, "I always keep the dressing room bed made up so I at least pretend we sleep in separate rooms. Isn't that enough?" While we may think married couples sleeping in separate beds is old-fashioned, having two twin beds instead of a double bed was actually a trend popularized by interior decorators in the 1890s. Queen Victoria and Albert were among the upper class couples of the time to sleep in separate beds, and even today Queen Elizabeth II and Prince Philip are known to have this arrangement.
At the end of the first season, youngest daughter Lady Sybil Crawley is paraded out in London during "the season" as a young woman ready for marriage. For women in the Edwardian period, this status was marked by pinning your hair up at 18. Before that age you wore your hair down as a sign that you're still a girl, but after 18 you're never to be seen in public with your hair down.
It's no wonder valet John Bates doesn't want to show affection for housemaid Anna Smith throughout the first season, despite being in love with her. During this period it was extremely off limits to get involved with fellow servants, and they prevented this by keeping male and female servants in separate quarters. Many times a romance between staffers would be blamed on the women, and could get you fired. We see an example of this when one of the characters gets pregnant in the second season.
Robert and Cora Crawley have their disagreements and issues (especially in season two), but overall have a loving relationship. But even if the marriage was in shambles, it's unlikely Cora would leave Robert due to the rules of marriage and divorce during this time. If a husband cheated on his wife, this wasn't grounds for divorce unless he left her as well. But not the case if the roles were reversed. Women who cheated on their husband could be divorced easily. And however it began, women would always be left high and dry after the split, with men getting sole custody of the kids and all joint money.
When the middle-class lawyer Matthew mentions working at the estate on the weekends, the Earl's mother Violet Crawley replies, "What's a weekend?" While the older generation of high-class women clearly had no idea what a 9-5 job was, their granddaughters most definitely would. The 1910s was the first time wealthy young women began attending college and seeking careers outside of finding a husband.
Another sign of the times changing for women was when Sybil went to get fitted for new clothes and scandalously chose a pantsuit. The Edwardian period was also the last era when women still wore corsets. In many ways this freedom of fashion expression would mimic women's freedom in general.
Once World War I was underway in 1914, more than five million women out of the 23.8 million women in Britain were working. And thanks to women's continued involvement in the war and political decisions following its end, the Suffragettes movement got a small boost from the war and its aftermath.
The Sex Disqualification (Removal) Act 1919 made it illegal to prevent a woman from getting a job based on her gender, and the Representation of the People Act 1918 gave women the right to vote for the first time, although British women would have to wait another decade for equal voting rights to men. Still, if the war did anything good for the women's rights movement, it showed women what they were capable of and got them out of the house and working.