American Christians who are most preoccupied with sexual morality tend focus on homosexuality, pornography, sex before marriage, etc. Except for the Catholic Church, we don't hear much about divorce and remarriage (and even American Catholic leaders don't say much that is covered in the media). Why? Some Christians do argue against divorce, but even they don't claim that remarriage is a sin. According to the Biblical texts, though, it probably is.
Read Article: Why Do Christians Allow Divorce & Remarriage?