Australasia had previously reached an agreement with the British Empire, so Australasia's demands were supported by the other three major powers of the Allies.
Facing the joint demands of the Allies' four major powers, Argentina had no ability to resist. After long negotiations, they finally agreed to Australasia's demands.
Argentina's black land is mainly concentrated on the Pampas plains. The black land here has a feature; it is primarily red oxidized black soil.
The surface of this black soil is red soil. Underneath the red soil is the real black land. The disadvantage is that it is not as fertile as regular black soil.
Moreover, developing agriculture on this black soil has a drawback – it is prone to causing soil erosion and damaging the soil.
None of these issues are problems for Australasia. Arthur wanted to obtain this land in order to build a granary in the short term, preparing for grain storage during the two wars.