I'm not entirely sure which 'second marriage webtoon' you mean, since there are a few with similar premises in the romance or drama sections, like 'The Remarried Empress' or maybe 'Marry My Husband'. But if you're talking about 'The Remarried Empress', that's the one I've actually read. The core of it is about Empress Navier who gets divorced by her emperor husband because he wants to marry his mistress. Instead of crumbling, she accepts a marriage proposal from a neighboring emperor, Heinrey, who's been interested in her for a while.
The plot really revolves around her navigating this new political marriage, rebuilding her power and status in a foreign court, and dealing with the fallout from her old life. A huge chunk of the tension comes from her ex-husband, Sovieshu, and his new wife, Rashta, constantly causing problems that spill over into her new kingdom. It's less about the romantic fluff of a new marriage and more about a strategic alliance that slowly becomes genuine, all while she outmaneuvers her enemies with sheer competence. The appeal is definitely in watching Navier stay composed and brilliant while everyone else loses their minds.