Another large wave took place in the Interwar period, as well as during and after World War II.

[2] In January 1928, a Polish expedition headed for the area of the Ucayali River, to check possibilities of creation of settlements for farmers on several thousand hectares of rainforest.

Soon afterward, the first settlers arrived in Peru, but because of the Great Crisis, the government in Warsaw ceased to fund the action.

Private donations were insufficient, furthermore, the first settlers discovered the local condition to be much worse than advertised.

In 1933, the contract with the Peruvians was terminated, and to avoid international scandal, all settlers returned to Poland.