Why "had" instead of "has"?

Maple wrote:

It is no accident that the twentieth century should be the century of highly centralized governments and totalitarian dictatorships; it had to be so for the simple reason that the twentieth century is the century of planetary overcrowding. (the essay was written in the 20th century) Why did the author use "had" instead of "has"? Is it a kind of subjunctive?

Not a subjunctive.  I think it should be 'has'.

Marius Hancu wrote:

EDIT: Philip has a point with has it's the correct version, as I don't see any IFs around.

You can only use had if there "IFs" around? Thanks

Hi everyone

Using "has to" in the sentence would sound strange to me.

I think the writer probably used "had to" because saying "has to" sounds like a reference to the future.  However, the writer is not referring to the future.  Although the century was not yet finished when the sentence was written, I assume it was written in the latter part of the twentieth century. The writer sees the twentieth century as having already become and already come to be seen as this "type of century".  And the things that have happened had to happen due to the fact that the century is also the century of planetary overcrowding (a fact which was already known when the sentence was written). 

Just my two cents. 

EDIT:
Oops, Jim posted while I was writing.   Looks like we see things the same way.

I think the author is saying that it was a foregone conclusion that the twentieth century was already the century of highly centralized governments and totalitarian dictatorships at the time of writing.  By saying it had to be so, he is referring to a time before the twentieth century became that way; he is referring to what preceding causes made it so.  (No subjunctive here.)

I think the writer probably used "had to" because saying "has to" sounds like a reference to the future.  However, the writer is not referring to the future. ........And the things that have happened had to happen due to the fact that the century is also the century of planetary overcrowding.........

These explanations make me start to understand it in some degree. Thanks a lot!

BWT: MH, Could you please tell me what is "IF" ? I'm a little curious about it. Thanks!