jahenders
Banned
I don't think you could effectively criminalize monogamy since it's the state one would be in when the first got married (unless they acquired multiple spouses at once) and if other spouses died.
However, you could make it taboo for someone to not consider taking additional spouses if the situation warranted it. For example, if after a major war, you had a high percentage of widows and women with no prospects, then any man who can afford to do so, should be willing to take additional wives and his wife should encourage him doing so. If they don't, then he might be considered selfish for wanting to retain more of his wealth and/or she might be considered selfish for not being willing to share her husband (and his wealth/time).
As some have noted, that could theoretically work both ways. If, instead, a situation arises where you have considerably more men than women, then women might be expected to take multiple husbands (and their first husband encourage them to do so).
BTW, there was an interesting SF book years ago that mentioned the multiple wives scenario, but it was only in the case where a guy died. Then his brother, or other kin, were obliged to take his wife (and children) as his own. So, it was only necessity based. I can't recall the name for sure.
However, you could make it taboo for someone to not consider taking additional spouses if the situation warranted it. For example, if after a major war, you had a high percentage of widows and women with no prospects, then any man who can afford to do so, should be willing to take additional wives and his wife should encourage him doing so. If they don't, then he might be considered selfish for wanting to retain more of his wealth and/or she might be considered selfish for not being willing to share her husband (and his wealth/time).
As some have noted, that could theoretically work both ways. If, instead, a situation arises where you have considerably more men than women, then women might be expected to take multiple husbands (and their first husband encourage them to do so).
BTW, there was an interesting SF book years ago that mentioned the multiple wives scenario, but it was only in the case where a guy died. Then his brother, or other kin, were obliged to take his wife (and children) as his own. So, it was only necessity based. I can't recall the name for sure.