I am reading "Can We Still Afford to Be a Nation of Immigrants?" by David M. Kennedy.

In the past three decades, since the passage of the Immigration and Nationality Act Amendments of 1965, the first major revision in American immigration statutes since the historic closure of immigration in the 1920s, some 20 million immigrants have entered the United States. To put those numbers in perspective: prior to 1965 the period of heaviest immigration to the United States was the quarter century preceding the First World War, when some 17 million people entered the country, roughly half the total number of Europeans who migrated to the United States in the century after 1820, (along with several hundred thousand Asians).
(This part can be found in the link above.)

I cannot fathom the meaning of the underlined phrase.

quarter century: 25 years --- right?
WWI happened during 1914 and 1918.
How come 1965 preceded 1914?

I think "prior to" can only be followed by noun or noun phrase.
How come there is a "was"? Emotion: thinking

Can anyone please enlighten me?

Best Regards

So the quarter century preceding WWI would be from 1889 to 1913. The "three decades following the act of 1965 would be 1966 to 1996.
We're talking about two different periods of heavy immigration, 1889 to 1913, and 1966 to 1996. The first one was prior to (before) the second one.

Prior to this year, the worst financial collapse was in 1929.

The earlier heavy immigration preceded WWI. The later heavy immigration followed the N.A.A. of 1965. The earlier one was prior to the later one.

Prior to Sarah Palin, the only woman to run in a general election for Vice President of the US representing one of the major parties was Geraldine Farraro. (How far away does the "was" have to be?)
A quarter century is 25 years, yes.

The highest rate of immigration to the US was during the 25 year period before WWI. This statement only refers to immigration rates prior to 1965.

Prior to (the year) 1965...

Which period are we talking about? It's the period that was prior to WWI.
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Ah...it did not occur to me that I should put "the year" before "1965."
I understand now. Thank you!
 Avangi's reply was promoted to an answer.
Thank you, Avangi. [8]
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