Complex sentence: The stagnation phase is characterized by a lack of good investment opportunities that leads to low interest rates and lowered credit standards which creates a speculative boom and high debt levels, followed by a crash and financial crisis.
Split into simpler sentences: The stagnation phase is characterized by a lack of good investment opportunities that leads to low interest rates. Sometimes low interest rates leads to lowered credit standards which, in turn, creates a speculative boom and high debt levels, followed by a crash and financial crisis.