It is in present day Belgium.
Belgium
The Battle of Waterloo was fought at Waterloo, Belgium.
Present day Belgium
Prussia
Present day Belgium south of Brussels.
The country is now called Belgium, but in Napoleonic times was part of the Low Countries (separated into Belgium and Holland a few years later). Waterloo is a few miles South of Brussels, which is the capital of Belgium. Waterloo was Napoleon's final battle.
belgium
Russia and Great Britain (who eventually defeated him at Waterloo)..
No country is known as 'water loop'. Perhaps you mean Waterloo, which is a Belgian municipality. This was the site of a battle that officially ended the rule of Napoleon. Although I've never heard of Belgium being nicknamed 'Waterloo', I suppose it's possible.
Waterloo, Belgium: 29,593 (2009) Waterloo, Ontario, Canada: 121,700 (2010) Waterloo, Quebec, Canada: 4,112 (2006) Waterloo, Iowa, USA: 65,406 (2010) Waterloo, Illinois, USA: 7,614 (2000) Waterloo, Wisconsin, USA: 3,259 (2000) Waterloo, Indiana, USA: 2,173 (2009) Waterloo, South Carolina, USA: 203 (2009) Waterloo, Oregon, USA: 239 (2000) Waterloo, New York, USA: 4,962 (2000)
It was in Waterloo, Belgium.