Overwhelmingly means to such a great degree that nothing else really matters or compares. When something happens overwhelmingly, it's so strong, so clear, or so complete that it dominates everything else.

If a candidate wins an election overwhelmingly, they crush their opponent by getting far more votes, perhaps winning 70% to 30%, or even more lopsided. If students overwhelmingly prefer pizza over salad for lunch, it's not a close call. Maybe 95 out of 100 students choose pizza. The preference is so strong and one-sided that there's no real contest.

The word suggests a force or amount so large it almost pushes everything else aside. A powerful wave might overwhelm a small boat. In the same way, when evidence points overwhelmingly in one direction, it's so strong and clear that doubt becomes almost impossible. When you feel overwhelmingly tired after a long day, the tiredness is so intense it overshadows everything else you feel.

Notice how the word turns something into an unstoppable force. An overwhelming majority means so many people that the outcome feels inevitable, like trying to stop an avalanche with your hands.