It might be a hard concept for this generation to fathom, but what we've come to know as a master bedroom has only been a common finding in real estate for the last few decades. The master bedroom has evolved greatly over the centuries.
Most American homes in the 18th and 19th centuries were totally utilitarian. Every square foot had a useful, practical purpose. Although the very wealthy often had multiple bedrooms, most Americans, especially those in colder climates, only had a single bedroom for the entire family. A family felt fortunate if they had one bedroom for the kids and one for the parents. These bedrooms were tiny so that they would better retain the warmth from their only source of heat, a fireplace.
It's actually alternative heat sources, mainly central heating in the late 19th century, that prompted rooms to become larger. Even with central heating, most master bedrooms still weren't as they are today. With the exception of the very wealthy, most Americans were simply too busy working very long hours to view their homes as anything other than shelter.
The master bedroom really began to evolve from a place of shelter to a place for retreat and respite with the introduction of the 40-hour work week. Average Americans finally had enough relaxation time to view their bedrooms differently. The 1950s saw a significant growth spurt in the number of middle class Americans, and master bedrooms started to get larger.
The 1970s gas and energy crisis caused many people to temporarily view large houses as energy money pits. However, gas and energy prices stabilized by the mid-1980s. In fact, it was in the mid 1980's that the super-sized, modern master bedroom really emerged. McMansions started popping up across the country as large sections of land opened up to form suburban neighborhoods and big single-family lots.
Throughout the 1990s and early 2000s, master bedrooms became suites with walk-in-closets, sitting areas, over-sized tubs, steam showers, and double sinks.
Even today, the master suite continues to evolve. One current trend is a master suite on both the first and second floors of a home. This is popular among homeowners that plan to stay in their home indefinitely, but fear not being able to safely climb the stairs as they age. These homeowners can put the first floor master suite to good use as a guest or mother-in-law suite in the meantime. It's also a popular trend among parents wanting to be near a child's second floor bedroom when they're young, but not quite so near them as they become teens. Another master suite trend is switching from the typical combination of an over-sized tub and small shower -to- a smaller tub and over-sized shower.