 The power of the Yemeni Zaidi State or Imamate declined in the 18th and 19th century, especially in the wake of the Wahhabi invasions after 1800.The territory controlled by the imams shrank successively after 1681, and the lucrative coffee trade declined with new producers in other parts of the world.The Qasimid state or Yemeni Zaidi State has been characterized as a "quasi-state" with an inherent tension between tribes and government, and between tribal culture and learned Islamic morality.