The question asks for a common institution among Nepal, Saudi Arabia, and Sweden. Historically, all three nations have functioned under monarchical systems. While Nepal transitioned to a republic in 2008, the question likely refers to their historical commonality or a specific context regarding the persistence of traditional executive structures. Saudi Arabia remains an absolute monarchy, and Sweden maintains a constitutional monarchy, making 'Monarchy' the intended answer in this comparative political context.

Nepal adopted its new constitution on September 20, 2015, marking a significant transition from a monarchy to a federal democratic republic. This document was the result of years of deliberation by the Constituent Assembly, aiming to institutionalize the political changes that followed the end of the decade-long civil war and the abolition of the monarchy in 2008.

Nepal transitioned from a monarchy to a democratic republic in 2008. This historic change followed the abolition of the 240-year-old monarchy by the newly elected Constituent Assembly, which was a result of the Comprehensive Peace Accord that ended the decade-long Maoist insurgency and paved the way for a new political order.

George W. Bush served as the 43rd President of the United States from 2001 to 2009. He won the 2000 presidential election and was re-elected in 2004. His administration oversaw major events including the September 11 attacks, the subsequent War on Terror, and the 2008 financial crisis.

Barack Obama was inaugurated as the 44th President of the United States on January 20, 2009. The oath of office was administered by Chief Justice John Roberts at the U.S. Capitol in Washington, D.C., marking the official commencement of his first term in office following his victory in the 2008 presidential election.

Barack Obama was inaugurated as the 44th President of the United States on January 20, 2009. This date follows the constitutional mandate for presidential inaugurations, which occurs every four years. The ceremony, held at the US Capitol, marked the peaceful transition of power and the beginning of his first term in office following his victory in the 2008 general election.

The 22nd Amendment to the US Constitution limits the President to two terms. Similarly, the French Constitution, following the 2008 constitutional reform, limits the President to two consecutive five-year terms. In contrast, the Indian President and Vice-President are not subject to term limits under the Indian Constitution, allowing them to seek re-election indefinitely if they continue to meet the eligibility criteria.

Abu Ali Hassan ibn Ali, famously known as Nizam al-Mulk Tusi, was a renowned Persian scholar, vizier, and author of the Siyasat Nama. Historical records generally cite his birth year as 1017 AD (408 AH) in the region of Tus, located in modern-day Iran. He played a pivotal role in the administration of the Seljuk Empire.

Nizam al-Mulk Tusi, in his famous work 'Siyasat Nama' (Book of Government), extensively discussed the role of the ruler and used the Persian title 'Padshah' to refer to the sovereign, reflecting the influence of Persian administrative traditions on Islamic governance.

Nizam-ul-Mulk Tusi was a prominent Persian scholar and vizier of the Seljuk Empire. He is celebrated for his profound political wisdom, most notably documented in his work 'Siyasat Nama' (Book of Government). His writings provided a comprehensive framework for statecraft, administration, and the ethical conduct of rulers, which influenced Islamic political thought for centuries.