because
This expression is used to explain the reason behind a situation, often implying that it was unavoidable.
Examples
遅れたのは交通が混んでいたものだから。
I was late because the traffic was congested.
問題があるのは彼女のせいではないものだから。
The problem isn't her fault, that's for sure.
私の都合で変更したものだから、理解してほしい。
I changed it because of my circumstances, so I hope you understand.
Quick check
I was late because the traffic was congested ___.