A brit, a froggie and a Yank found a bottle with the usual genie.. one wish, blah; blah, blah.
The yank want's americas farmland fertile forever.
the frog wants an impregnable wall around france, so france never need worry about invasion again.
the brit asks the genie 'how high's this wall around france? 50' sez the genie. The brit thinks a moment and sez.. 'well, mate; then I suppose for my wish, I'd like to see that filled with water.'