Judaism
Christianity was originally a sect of Second Temple Judaism, but the two religions diverged in the first century. The differences between Christianity and Judaism originally centered on whether Jesus was the Jewish Messiah but eventually became irreconcilable. Major differences between the two faiths include the nature of the Messiah, of atonement and sin, the status of God's commandments to Israel, and perhaps most significantly of the nature of God himself. Due to these differences, Judaism traditionally regards Christianity as Shituf or worship of the God of Israel which is not monotheistic. Christianity has traditionally regarded Judaism as obsolete with the invention of Christianity and Jews as a people replaced by the Church, though a Christian belief in dual-covenant theology emerged as a phenomenon following Christian reflection on how their theology influenced the Nazi Holocaust.
Islamic schools and branches
Shia Islam, on the other hand, is separated into three major sects: Twelvers, Ismailis, and Zaydis. The vast majority of Shias are Twelvers (a 2012 estimate puts the figure as 94% of Shias being Twelvers) to the extent that the term "Shia" frequently refers to Twelvers by default. The Twelver Shias are also notably the only sect of Muslims that complies with the saying of Muhammad that he would have twelve successors, a saying accepted by both Shia and Sunni Muslims.