Complex sentence: Huntington argues that those changes are caused by tensions within the political and social system, and criticizes modernization theory, contending that its argument for economic change and development being the prime factors responsible for the creation of stable, democratic political systems is flawed.
Split into simpler sentences: Huntington argues that those changes are caused by tensions within the political and social system. Huntington criticizes modernization theory, contending that its argument about economic change and development being the prime factors responsible for the creation of stable, democratic political systems is flawed.