It is the battle too because it was the first time Wellington actually commanded an army in the field against Napoleon himself. In Spain, Wellington was opposed by Napoleon’s Marshalls. Many thought that the Duke of Wellington could not actually beat Napoleon in a battle one on one. And even now who can say, because it took the return of the Prussian Army under Blucher to defeat Napoleon at Waterloo. It wasn’t looking so good for Wellington at the time pre-Blucher.
Napoleon knew the Prussians were coming and could not beat Wellington in time to deal with them thus Wellington beat Napoleon. He was a better General and better man than Napoleon in my opinion. I’ve tried to read histories of Napoleon but the guy makes me sick. You can get some good histories of Wellington. Napoleon was a complete megalomaniac who didn’t give a damn about his soldiers. He had many close calls of his own and was lucky to have such a fiercely nationalistic army.
Wellington's forces were positioned all along the line with HIS most trusted groups in strategic places to assure the line would hold.
The troops who were experienced and proved loyal had been with him in Portugal. They were placed in the line where their refusal to retreat would be an example and foil to others who might be tempted to back down.
Also, Wellington picked that low ridge because for miles around (in a very flat topography) it was the only terrain that resembled high ground ... AND which had trackless forest immediately behind. He felt this too would discourage retreat, as his troops would find NO easy way off that ridge, in their rear.
The British had been (even up to Waterloo) plagued with en masse, battlefield desertions of whole regiments which were made up of coalition, non British forces and were not to be trusted. The famous 'sunken road' or the Ohain Road right in front of, and nearly parallel TO the British line, was a nasty surprise for the French. It was something they SHOULD have scoped out way in advance of the fight... BUT Marshal Murat wasn't there, sooooo.....