There are several related definitions for this word. One is a "general breakup or sudden collapse of something. e.g.
After many years of separation between East Germany and West Germany, a great social and political debacle allowed Germans to travel freely between the East and West, ending years of separation"
Another definition is " a violent rush of water or ice". e.g.
A great debacle destroyed the seaside village, as the first tsunami in over fifty years visited this tiny island nation.
The other definitions focus on a defeat, failure or fiasco:
The political clash over financing health care became a complete debacle in the legislature.
The king's forces were undefeated until a debacle at the enemy fortress.