All Eurozone countries have the right to make special euro coins, but the other countries have to agree with them. The French government did not want to be reminded of Napoleon’s defeat 200 years ago, and objected.
The Belgian government has now decided to make the Waterloo commemorative coins 2 euro 50 coins, not valid for paying in shops. For such coins they do not need other countries’ permission.
Napoleon’s defeat at Waterloo caused in part by Indonesian volcanic eruption: here.