While the troops coming from the Kingdom of the Waves were moving only a few weeks away from the Black Plain, the troops from the Kingdom of the End of the Snow Kingdom were also not far away.
In the case of the troops coming from the Kingdom of the End, since the distance between this state and the Black Plain was too great, they traveled much of the why by ship. That was something that could transport them with more safety and a speed similar to the low-level beasts used by that state's organizations.
And with that, they were already landing their troops in the Peninsula of the Waves, from where they would proceed overland to the Black Plain.
After all, there was a naval fleet around the Black Plain; while coming by land from the south of that state, they could enter the part of the enemy territory under the command of the allied forces.
That way, it was more worthwhile to finish that part of the journey by land!