Complex sentence: His political rivals had blamed his socialist policies for slowing down Pakistan's economic progress owing to poor productivity and high costs although Bhutto and his colleagues maintained that Bhutto was merely addressing the massive inequality built up over the Ayub Khan years.
Split into simpler sentences: His political rivals had blamed his socialist policies for slowing down Pakistan's economic progress, as they caused poor productivity and high costs. However Bhutto and co countered that they were mere addressing the massive inequality built up over the Ayub Khan years.