why did the dark lord make the one ring?

[Hot, crispy nice hobbit]

Actually, Sauron could have crushed them all even without the ring. Gandalf said this:

"Hardly has our strength sufficed to beat off the first great assult. The next will be greater. This war then is without final hope, as Denethor peceived. Victory cannot be achieved by arms, whether you sit here to endure siege after siege, or march out to be overwhelmed beyond the River. You have only a choice of evils; and prudence would counsel you to strengthen such strong places as you have, and there await the onset; for so shall the time before your end be made a little longer.

Let's face it. Near the End of the Third Age, all the forces of Good are so rusty that you can practically crumple them with a poke of the finger. If not for Gandalf, I hardly think that Sauron can be defeated, with or without his ring.