Once, in ancient times, there were two neighbouring kingdoms who had, since Time Immemorial, continued a border war.
No one could be found in either the Kingdom of Tar or the Kingdom of Ory to tell why the war had begun in the first place or why it continued. The two kingdoms were implacable enemies.
In the spring of one year, both kingdoms had much more rain than usual. Day after day of rain saturated the farm lands of both Tar and Ory, and an enormous crop of weeds sprang up, hindering the spring planting and threatening both kingdoms with starvation.
Something had to be done. Emissaries were sent to arrange a truce between the two kingdoms so that the soldiers could help with ridding the fields of each kingdom of the plague of weeds.
The truce went so well that the emissaries agreed that the soldiers of each country would help the other get rid of their weeds.
Suddenly the thoughts of war were over for the first time in living memory, the weeds were destroyed, and the two kings held a great celebration in which their peoples found out they rather liked each other, after all.
So, replacing the tradition of war between the two kings, the great Spring celebration was held every year, thereafter, and the Kings became known as The Weed-free Kings of Ory and Tar.
Clever.