Usage and Grammar
Q. When referring to a decade, do you use “was” or “were”? “The 1780s was [were?] an important period in history.”
A. Aside from certain quantities (“ninety dollars is a lot of money”), plural numbers usually take plural verbs: for example, “The ’80s were great!” To be perfectly correct, then, avoid the lure of the singular “period” in the predicate and use “were”: “The 1780s were an important period in history.” Compare “The decade of the 1780s was an important period in history.” See also CMOS 5.141 (on false attraction to the predicate).