The great director, Elia Kazan (Zapata!, On The Waterfront), made it a habit to condense a movie script down to one sentence. That way he could understand what the story was really about and anything that didn't adhere to that one-sentence-idea was stripped away.
I decided this is a good exercise. So I took a handful of movies that popped into my head and gave them the one sentence treatment:
• Tombstone: two gangs collide in a frontier town.
• McCabe & Mrs. Miller: An ambitious gambler gets in over his head.
• The Searchers: A racist loner seeks revenge but finds redemption.
• 26 Men: A handful of Arizona Rangers saddle up to solve crimes in the vast Arizona Territory.
• Hell Or High Water: A retiring Texas Ranger tries to catch two brothers who are losing the family farm to a crooked bank.
• Once Upon A Time In The West: The railroad brings woosies.
Now you may disagree with me on some of these, especially the last one, but I was merely taking my cue from Sergio Leone himself:
—Sergio Leone, explaining the ending of Once Upon A Time In The West