The biblical land of Sheba is modern Yemen. There's evidence of occupation in the area from 5000 BC onward with civilization flourishing somewhere from 800 BC onward. These people went from polytheism to Judaism, then to Christianity around the 300s AD, and then to Islam in the 600s AD. These were a people never conquered by Romans, Byzantines, or Persians despite their attempts. They controlled a large amount of trade through the the waters surrounding their country and were prosperous in their time.
The location of Yemen did, however, make them a target of the Ottoman Empire. From the early 1500s through the mid 1700s, the Ottomans gained and lost ground repeatedly.
By the mid 1800s, the Ottomans were absent from Yemen and the British had arrived. They took control of a large amount of Yemen called the Aden Protectorate, and used it for the servicing of ships as well as for its resources. This became more important with the opening of the Suez Canal. The area immediately surrounding the city of Aden was given autonomy and protection so long as they didn't trade or have other dealings with foreign powers.
British presence and the canal brought the Ottomans back to the area. The Ottomans took control of the rest of Yemen (mostly) and remained in control of that territory until 1911 when a series of revolts were simply to costly for them. The rest of the Ottoman holdings left in 1918 with the fall of the Ottoman Empire.
With the Ottomans gone, there were two distinct states. There was the Yemen Kingdom in the North West and Aden in the South East. In the 1960s, the North had a civil war which created the Yemen Arab Republic, and the South had a civil war that ended British presence and created a marxist People's Democratic Republic of Yemen. These two new states then went to war on and off through the 1970s with considerable interference from foreign powers. The 1980s saw continued fighting between the two, but less often, and the South had a civil war. Unity was achieved 22 May 1990.
Unfortunately, the unity of the two states didn't achieve the peace for which many hoped. Civil war broke out again in 1994. This civil war resulted in many of the socialists and marxists from the South being exiled.
Up to this point, the history of Yemen is reminiscent of many other former colonial holdings and of the nations resulting from the breakup of the Ottoman empire. There was a long history of a people and the development of their culture and traditions, but due to location they were absorbed by foreign powers. Those powers leave and the people are now fractured and warring. Eventually, stability emerges as the people solve their differences.
Ali Abdullah Saleh became Yemen's first directly elected President in 1999. By this point socialism and civil war had placed Yemen among the poorest of nations on Earth, and there was still trouble ahead. In October 2000, there was a suicide attack by al-Qaeda on the USS Cole which was in Aden. Later Yemen became a US ally in the War on Terror following the events of September 11 2001.
A Shia insurgency was started in 2004 by cleric Hussein Badreddin al-Houthi (leader of a Shia sect, Zaidi).
In 2009, the Yemeni and Saudi branches of al-Qaeda merged to form al-Qaeda in the Arabian Peninsula. Their attacks continued despite some give on President Saleh's side.
Despite the Shia insurgency and the Sunni al-Qaeda insurgency, Saleh was re-elected. His turnout was diminished. In his first election, the results were nearly unanimous. This time he received about two thirds of the votes.
Also in 2009, the Yemeni army began a fresh offensive against the Zaidi Shia Houthis. This was with the support of the Saudi government. Tens of thousands of already impoverished people were displaced in that fighting. While a cease-fire was reached in 2010, the Saudi assistance proved to be a bad move. The Houthis claim that Saudi Arabia had been providing support to Salafi groups in Yemen to suppress Zaidism. This really wouldn't be out of character for the Saudis anyway. US drones and cruise missiles began operating in this conflict in December 2009.
In September of 2011, Anwar al-Awlaki and Samir Khan (both US citizens) were killed in drone strikes without a trial while in Yemen. US citizens were killed without trial on foreign soil, by a US President's order. This was followed in October 2011 with the murder of Anwar's 16 year old son, Abdulrahman al-Awlaki.
Also in 2011, following the Tunisian uprisings, mass protests developed in Yemen. The main complaint was Saleh's three decade long rule and perceived lack of democratic reform. It would appear that these protests and uprising were the result of the work of Hamid al-Ahmar, leader of Islah political party, a prominent businessman, and the leader of Yemen's largest tribal confederation. He apparently planned, funded, and organized the protests in Yemen with the aim of removing Saleh from power.
In 2012, after siding with the Houthis against al-Qaeda, the Saudis and other Salafi groups, Saleh was removed from office and replaced by Abdrabbuh Mansur Hadi. US Special forces and the CIA arrived around this time.
As of 2015, Saleh loyalists, the Houthis, and the Republican Guard have been fighting the Islamic State, the Saudi Arabian led Coalition (including US special forces, cruise missiles, drones, etc...), and al-Qaeda. Once again, the USA is taking of the side of Islamic State, Saudi Arabia, and al-Qaeda.
On January 29th of 2017, Nawar al-Awlaki an 8 year old girl and US citizen was shot through the neck by US special forced in Yemen. She suffered for two hours and died. She was the daughter of Anwar al-Awlaki and the sister of Abdulrahman.
As noted previously, Yemen was already among the poorest nations on Earth prior to this war. Due to Saudi coalition bombings of civilians and the blockade, more than 22 million people in Yemen are dependent on humanitarian aid, and roughly 16 million people cannot get access to potable water. There have been more than 900000 cases of cholera in Yemen as a result of this.
Three years of constant war with intermittent violence between the involved groups prior... what makes anyone think that peace will be a achieved? Families have been slaughtered. You cannot kill someone's children, spouse, cousins, neighbors during an invasion and somehow think that these people will welcome you as anything other than an invading force of demons. You cannot shoot 8 year old children and think people will believe you when you say that you are present in their homes for their benefit. That isn't how people work. When you take actions like this, you create more enemies. Iraq, Libya, Syria, Afghanistan, Yemen... The people of these nations will never like the USA and her allies. Immoral behavior leaves an imprint.
The campaign in Yemen is an atrocity. It is an unprovoked aggression against a nation that was a US ally in the War on Terror. The Saudis and the USA have invaded a poor nation, bombed its civilians, and allowed disease and starvation to spread rampantly through the population. This is a crime against humanity: millions displaced, millions starving, and a million with cholera. And through it all, the Saudis and the USA have been on the side of al-Qaeda and ISIS. I suppose this is simply how the USA treats her allies.