I did a search here and its been asked a few times but responses were pretty weak. But what really caused it? I've been reading about the whole age of exploration, Portuguese, Spanish, Dutch, French and English. The trade that occurred during that period is a lot more problematic then is really discussed. Typically the Europeans didn't have much that other countries were interested in trading for. To make the economics work it turned into a more militaristic tribute trading system, colonial system, and mercantilism. I asked this on the history reddit and proposed my theory, that it was because the railroad was a cheaper way to move goods than ships so countries like the US, Germany and Soviet Union economies grew faster. Results of the discussion were pretty unsupportive.

Here's the thread if you wish to read further:

https://www.reddit.com/r/history/comments/4f0b2d/cause_of_the_fall_of_british_empire_steam_ships/