Like others have said, depends on what the magic is capable of, but I would give the advantage to the modern military. Could a dragon or griffon stand up to modern fighter jets who are able to fly faster and higher? Could a magical ground force withstand modern artillery and/or bombers? Could they produce shields or other countermeasures to protect themselves from those kinds of munitions? How would archers and mages fare against modern rifles that could engage them from hundreds of yards/meters away? Also, the greatest weapon in any war is information. The modern military (assuming the battlefield is somewhere on Earth) would have access to real-time info from satellites, radar, etc. Would the magical military have anything similar?
Like others have said, depends on what the magic is capable of, but I would give the advantage to the modern military. Could a dragon or griffon stand up to modern fighter jets who are able to fly faster and higher? Could a magical ground force withstand modern artillery and/or bombers? Could they produce shields or other countermeasures to protect themselves from those kinds of munitions? How would archers and mages fare against modern rifles that could engage them from hundreds of yards/meters away? Also, the greatest weapon in any war is information. The modern military (assuming the battlefield is somewhere on Earth) would have access to real-time info from satellites, radar, etc. Would the magical military have anything similar?
All well and good until a wizard opens up a portal to the moon. Or the void just outside the observable universe