France's 10-year bond yield just hit 4.054% — highest since 2009.

The math is simple: France is running a 6%+ deficit, double what EU rules allow. Bond buyers are saying "if you want our money, you're paying up."

When a major economy like France sees yields spike like this, it's not just their problem. Higher borrowing costs ripple through European markets, affect the euro, and change how investors price risk across the board.

Watch how this plays out. If France can't get spending under control or growth doesn't pick up, these yields could go higher. And that puts pressure on everything from European stocks to the exchange rate.