Complex sentence: Although there are important disagreements, many scholars writing on the topic today begin with the premise that "secularism" is not simply the absence of religion, but rather a category that itself needs to be understood as a historical construction.
Split into simpler sentences: Although there are important disagreements, many of the scholars writing on secularism today begin with the premise that "secularism" is not simply the absence of religion. Rather, these scholars argue, the category itself needs to be understood as a historical construction.