The Great Schism
The Western Schism, also known as the Papal Schism, lasted from 1378 to 1417. It was a split within the Roman Catholic Church, where there were two or even three rival popes claiming authority. The Schism resulted in a decline of Church power as it weakened the credibility and unity of the Church, creating divisions among the faithful.
The guangxu reforms
The Taiping Rebellion was the result of a rebel government in Southeastern China lasted. It was one of the world's most bloodiest civil wars and lasted from 1851-1864.
The Great Depression.
It became clear that the nations that lasted the longest would win....apex
Up to 12 years in some states
Russia's war with Sweden, known as the Great Northern War, lasted for 21 years, from 1700 to 1721. The conflict ultimately resulted in significant territorial gains for Russia and marked the decline of Swedish influence in Northern Europe. The war concluded with the Treaty of Nystad in 1721.
The Battle of Ezra Church lasted from about noon to the darkness of July 28,1864.
The Peloponnesian War ended the golden age of Pericles. This conflict, fought between the Delian League led by Athens and the Peloponnesian League led by Sparta, lasted from 431 to 404 BCE. The war resulted in a significant decline in Athenian power, democracy, and cultural prosperity, marking a shift in the balance of power in ancient Greece.
In the US the "baby boom" resulted from the return of many soldiers from WW2 and getting married. This period lasted from 1945 into the early 1960s.
At the moment it was concluded they did, but that feeling only lasted a short time and the unintended results of their best planning resulted in World War One.
After the growth of the Ottoman Empire, the state had already reached its pinnacle. This led to the stagnation and decline of the Ottoman Empire, which lasted hundreds of years.