OPINION: Conservative monarchs have for decades ruled over the Persian Gulf states with absolute power, ensuring loyalty from their subjects and stability in a region vital to the world economy.

This has been especially true of Saudi Arabia, the world’s largest oil exporter, where sons of founding monarch King Abdulaziz have reigned since his death in 1953.

Relying on petrodollars and close political and military links with the US, they have managed to keep at bay hostile neighbours such as Iran and Iraq, while safeguarding their thrones through generous cradle-to-grave social welfare systems.

Neighbouring Kuwait also falls into that category. Its oil wealth prompted Saddam Hussein to seize control of the nation in 1990, triggering a global military response led by the US that helped drive out the Iraqi dictator a year later.

But the end game could now be in sight for the oil-fuelled era of prosperity that has played such a vital role in ensuring energy supplies to the world economy.

The Arab world’s oldest rulers, Saudi King Salman, 84, and Kuwaiti Emir Sheikh Sabah, 91, have just undergone surgery — King Salman had his gallbladder removed, with the Kuwait ruler flown to the US for further medical treatment.

Succession lines are clearly laid out in Saudi Arabia, where Crown Prince Mohammed bin Salman — known as MbS — is already ruling supreme, but the political fate of Kuwait is marked by deep uncertainty.

Sheikh Sabah’s 84-year-old half-brother, Crown Prince Sheikh Nawaf, is the designated successor, but given his advanced age is unlikely to remain on the throne for long.

As such, there are worries over a power struggle between the two major branches of Kuwait's ruling Sabah family — the Jaber and the Salem.

The end game could now be in sight for the oil-fuelled era of prosperity.

Kuwait's future is crucial to the power dynamics in the region, where dominant players Iran and Saudi Arabia came to a full-blown military conflict last September when missiles and lethal drones, said to have originated in Iran, knocked out almost half of Saudi oil production.

Ironically, that event prompted the United Arab Emirates — a staunch Saudi supporter — to rethink its anti-Iranian rhetoric and try to cosy up to Tehran.

A new Kuwaiti leader could choose to distance the country from 34-year-old MbS, who has involved Saudi Arabia in disastrous conflicts such as Yemen’s civil war, and encouraged the US to strengthen sanctions on Iran.

Kuwait has consistently followed the Saudi line on oil policy, but keeps close ties with Iran and Qatar, Riyadh’s major foes.

Since his father became king in 2015, MbS has taken charge of military, economic and foreign policies while cracking down on domestic foes. He has also bought popular support by easing social restrictions, such as allowing women to drive.

However, with low oil prices at risk of derailing his ambitious economic reforms, the authorities in Riyadh are considering taboo subjects such as the introduction of income tax.

Economic pressures are likely to strengthen MbS’ resolve to ensure oil prices are high, but they also threaten to upset the time-honoured tradition of buying the public's allegiance via lavish social spending.

As Saudi Arabia and Kuwait near the handover of power from ageing conservative leaders, collapsing oil revenues and the emergence of over-zealous young leaders such as MbS do not auger well for the future of absolute rulers of the Persian Gulf.

(This is an Upstream opinion article.)