For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Pierre, Natasha, Andrei, Nikolai, and Marya are all connected to inappropriate partners, mostly because of their youth and general inexperience, and also because of their individual personality quirks.
Act II
Napoleon's 1812 invasion of Russia disrupts everyone's lives, dramatically transforming each character's personality because of demanding new circumstances, and killing off Andrei.
Act III
After the war, those who have survived re-form into lasting and meaningful family bonds, rebuilding the domestic lives that have suffered upheaval.