More people = more tax = more money
More land = more people = more tax = more money
Unfortunately that's not how the world works. What contributes mostly to our debt is our healthcare programs, our social security program, our defense budget, income security programs, federal pensions, transportation expenses, education budgets etc.
You can't just tax the forget out of your citizens and expect that debt rift to close. Our best hope currently is to knock away sizeable chunks of debt until we're able to get it down to a manageable amount.
Also I just looked it up, apparently Belgium's current public debt is actually $478 billion.