Was Rin's death the only reason which has led Obito to start Fourth Great War? It seems like there weren't any other reasons for Obito to consider Mugen Tsukuyomi.

Did Obito had other motivation, except Rin's death?
Rin's death was just the final spark to make Obito start the Fourth Great War. His hatred towards "evil" shinobis, current world and the desire to fix the world were evident from a long while (him always trying to compete with Kakashi to get stronger and save his allies). He was searching for a way to bring "peace" to everyone which is when Madara came in, in the times of despair Madara presented him a hope of "Infinite Tsukuyomi" which to the strong desires of Obito looked like the perfect solution. I won't just call it manipulation, for that time, the goals of Madara and Obito were quite similar and it was more of an agreement than just manipulation. Madara found the perfect candidate to carry his will, Obito found the perfect solution he deemed "correct" in his twisted, despaired mind.