Nowadays they don't practice but their holy books some prophets are polygamist
By and large modern Judaism and modern Christianity do not promote polygamy, but historically both did. In either case, the two religions are similar in this respect.
In some religious teachings, such as those in certain branches of Christianity and Islam, polygamy is allowed or even practiced. However, other religions, like Judaism and mainstream Christianity, do not support polygamy. Ultimately, beliefs about polygamy vary among different religious traditions.
Christianity, Judaism, Islam and Bahai.
Judaism - the 'parent' religion of Christianity.
The main three would be Judaism, Christianity, and Islam.
Christianity and Judaism
Islam, Judaism and Christianity.
no where in the US is it legal to practice polygamy
Groups of Mormons that have splintered from The Church of Jesus Christ of Latter Day Saints allow polygamy. The main body of the church is in no way connected to what are called "Mormon Fundamentalists" and does not practice polygamy. Polygamy (specifically Polygyny or one man having more than one wife) is also permitted in most forms of Islam.
The significance is that it became the foundation of modern Judaism, Islam, and Christianity.
The Pope has called Judaism "Christianity's older sister," since Christianity bases much of its content on Judaism.
Christianity does not struggle with Judaism.