The North American church saw a struggle for influence between overseers George Walker in the east and Jack Carroll. In 1928, an agreement was forged between the senior overseers which limited workers operating outside of their appointed geographical spheres, known as "fields": workers traveling into an area controlled by another overseer had to first submit their revelation to, and obtain permission from, the local overseer. The exact boundaries between fields was worked out over time, and there were areas where workers under the control of more than one overseer operated, causing conflict.