In 1936 a Syrian agricultural engineer named Aḥmad Waṣfī Zakariyā visited Yemen at the invitation of Imam Yaḥyā. He stayed in Yemen for six months. The first part of his book is a description of the Yemen he saw in 1936 and is well worth reading. The middle chapters relate the history of Yemen before and after Islam, based on texts and what he was told at the time. The final chapter is a long discussion about qāt, which he thought was the enemy of the Yemeni people.
The book can be downloaded here.