Well, the term imperial comes from empire, so the imperial era lasted until no country had or was trying to gain an empire. You should take colonies into account, but it is important to recognize that WWII was an attempt by Germany, Japan, and co. to establish empires. By that definition, the modern imperial era extended from the 15th to the 20th century. You may also take into account the more ancient Roman, Persian, and French (Alexander the great) empires. I am fairly certain my answer will be supported by any history textbooks you may come across.
Imperial China lasted from about 221 B.C.E to 1644 C.E
they last like 65million years
Chinese society especially in the Imperial Era was known as a civil society.
forever
About 300 years
Around 70 years
almost 2011 years (its the era we are in)
The era lasted approximately 150 years.
20 years
Using an Imperial tsp, it should last 30 days.
The last czar (or, tsar) of Imperial Russia was Nicholas II (1868-1918). Deposed in 1917 by Communist revolutionaries, Nicholas II died one year later at the hands of the same revolutionaries, thereby ending the imperial age in Russia and beginning the Communist era.
This period lasted from about 1800-1850.