This is implausible. The world is not like your neighborhood, and a flooded poor country is not like a neighbor down-on-his-luck. Certain countries, such as China, could possibly raise a ruckus in the form of war. Regionally, a neighbor could as well (such as Mexico to the US) in the form of illegal immigration.
And a wall won't work against nukes does it? (or tunnels)
The 1% percent will be fine in there bunkers....for awhile.