Incels exist in both monogamous and in promiscuous/polygamous societies, but there are far more incels in the latter than in the former. Approximately
52% percent of 30-year-old American men have never married, compared to only
4.7-7.3% of 30-year-old Amish men. Unmarried is not the same as incel, but there is obviously a correlation.
In the 19th century,
13-14% of men were still unmarried by age 39, compared to
24% of men today. Even in the 19th century, there were women who had jobs and didn't need men to provide for them. Some of those women ended up delaying marriage indefinitely and pricing themselves out of the market. But the primary reason why some men were incels at the time is because they couldn't afford to get married and provide for a family. Today there is much less poverty, yet a higher percentage of men are celibate. This is because women today are more hypergamous than they were back then when they had fewer rights and were more dependent on men.
There have been times in history were male shortages as a result of war and where virtually every man who could provide for a woman could get one, but these situations were the exception rather than the rule. As long as women have rights and the gender ratio favors men over women, there will always be some men who will be incels. A permanent female surplus can only exist in a hardcore patriachal society where women and girls are property that can be bought, sold, and bred for profit in the same way that animals are bred for profit today. In such a society, the idea of there being "involuntarily celibate" men will sound just as absurd as the idea of there being "involuntary petless" men.
In the 19th century, there was not so much a "sexual marketplace" as there was a marriage market in which money played a bigger role than attractiveness. Inceldom and poverty overlapped much more strongly than is the case today. There was a lot of disdain towards poor and low-status males, not so much towards incels in particular, and some people were sympathetic towards men who couldn't afford to get married. In today's day and age, single men spend a lot of time competing for and pandering to women in the hope of getting sex or relationships, and are more likely to look at other men as rivals. Back then there were a lot of male-only spaces where lower status males could fraternize with each other. Women had not yet invaded and corrupted every part of public life.
Altright tradcucks are just racists who worship and idealize White women.
The alt-right is a modern movement that isn't really all that traditional. Traditionalists believe in male authority over women and female submission. The alt-right might encourage women to stick to their traditional gender roles, but they have no interest in forcing them to do so. They only expect men to stick to their traditional gender roles as providers. They are perfectly fine with "tradthots" being part of their movement. Some of them reject Christianity because they mistakingly believe White women were held in higher regard when Europe was still pagan.
The gynocentric chauvimism of the Klux Klux Klan, which in its early days had a large female membership, is
similar to that of the modern alt-right movement. In the early 20th century, the Klu Klux Klax supported female suffrage to reduce the political power of black men who had been given the right to vote after the Civil War.