In the previous thousands of years, women basically fell into four groups:
With civilization, the spacing of children came about through knowledge of sex as it relates to pregnancy. Also, when quality of life began to include livelihood and budgets, family planning became all the more prevalent in society. And then when the birth control pill was invented, technology drove that final wedge of convenience between sexuality and reproduction.
Early Hormone Management
When the birth control pill was first formulated, it was sequenced in such a way that the hormones would suppress ovulation for 21 days, but the last seven pills were placebo, allowing the hormone "withdrawal" that brought about a menstrual period. In this way, the woman taking them would know she wasn't pregnant and would be reassured that everything seemed to be working. She may have been correct in knowing she wasn't pregnant by the appearance of a period, but the bleeding assuring her that everything was working as usual was a false reassurance.
The truth is that from a menstrual cycle standpoint, nothing is working at all. Just the end organ, the uterus, is doing the bleeding. It's the pill that runs the show, successfully shutting down the pituitary influence on the hormonal cycle. But "periods" coming at the right time wouldn't raise any eyebrows, so it was a brilliant marketing move in the 1960s for the pharmaceutical companies to present their pills in such a way that regular monthly cycles were mimicked.
In the past, patients treated for PMS or debilitating pain during periods were offered a new way to take the birth control pill. They would be instructed to take the 21 active pills, but instead of proceeding on to the seven "sugar" pills and have a period, they would instead go right into the next pack of pills. A patient who did this would have a period after 42 days or so. A patient who did this four times would only have a period every three months. Eight continuous packs would keep periods down to twice a year. It was one of the best kept secrets in gynecology, because it was feared that patients would look at the suppression of periods as unnatural.
But isn't the suppression of ovulation just as unnatural? Yes. But since ovulation doesn't have an obvious outward sign (like bleeding), this unnatural suppression is forgiven every month by the woman who doesn't get pregnant.