What caused Frodo to finally give in to the power of the Ring and claim it?

[FerniesApple]

I think Tolkiens experiences in the trenches would have told him that sheer physical exhaustion, lack of sleep, hunger and fear itself can demoralize the strongest soldier. Hobbits being more resilient than men just lasted longer before the corruption entered his soul, and then like a dam bursting all at once the Ring held him in its grip. It could have felt in danger so put forth its last attempt to survive.