Zaidi Shia Imamate under the Hamidaddin dynasty (Imam Yahya, then Imam Ahmad), which emerged as an internationally recognized independent monarchy over North Yemen following the Ottoman withdrawal in 1918.
Overthrown by the 26 September 1962 Free Officers' coup, which proclaimed the Yemen Arab Republic; a Saudi-backed royalist rump continued fighting from the northern highlands through the North Yemen Civil War until a 1970 peace settlement formally dissolved royalist claims.
The atlas holds 4 border frames for Mutawakkilite Kingdom of Yemen — the shape you scrub through changes in 1918 · 1925 · 1934 · 1942.
Standard English-language political history covering exactly this kingdom's full lifespan (Imam Yahya through Imam Ahmad) through the 1962 coup and into the republic's first years. Open-Library-verified (numFound=6, consistent title/author/1967).