Yemen's First Civil War 1962-68
The current war in Yemen is about the worse of two evils- either support President Hadi or let the Houthis take control with Iran in the shadows. It is about Sunni versus Shiite, with Saudi Arabia being Sunni and Iran and Houthis being Shiite. It is about hate on both sides for each other. It's about geopolitical issues as Iran tries enlarge its influence in the Middle East.
The current Saudi bombing as had about 2500 sorties and logistical support from the USA and Turkey. They have deployed troops along the border. The Houthis have been able to make some attacks keeping the Saudis off balance.
In 1962, Abdullah al-Sallal, assaulted with supporters the palace of the last king, al-Badr. This coup promised to bring Yemen into the 20th Century. Al-Badr fled the palace and went hiding in the highlands with his supporters. The coup was fully supported by Egypt, then led by Nasser and they put together an international coalition. Egypt threatened to take the war to the Houthis into Saudi Arabia, which made the Saudis to support the Houthis! The Saudis provided them with munitions and money.
As the war developed, Egypt eventually sent in a total of 70,000 troops from just a few hundred. As the war dragged on, Nasser would tell the press that Yemen was "Egypt's Vietnam". The Egyptian army became mired down in the Yemen mountains where the Houthis are now. When aircraft bombed, many of them hid in the caves, immune to their effects. The Egyptian army had many problems in the mountains against the poorly armed guerillas- and remember, there was no al-Qaeda there then. Nasser even used gas to force them out of the caves, which failed. The odd thing is that the more Egypt bombed the Houthis, the more support left the Egyptians. By 1967, they found themselves supporting an illegitimate government. Then, Egypt invited the coup leader, Sallal to Cairo. Upon his arrival and meeting with Nasser, he was not allowed to leave for several months! But the loss to Israel after the 1967 war was a crushing blow and Egypt had enough of Yemen and began to withdraw troops. The coup leader, Sallal, was then tossed out of power and sent to Baghdad, Iraq. In 1968, the deposed leader and his followers were ready to take Sanaa back until a neutral leader, who had respect from both sides, reconciled and cobbled a new government.
In 2009, the Saudis invaded Yemen again when the Houthis, once gain, tried to gain power. That did not work out well. Now, the Saudis are following Egypt's path. It seems with each Saudi bomb dropped, the Houthis gain support on the ground. So far, Saudis have not sent troops into the mountainous area or anywhere in Yemen.
They are leery of the history!