Complex sentence: Stalin, who was consolidating his power over country, approved Yakir's appointment to Ukrainian Military District in 1925, but he did not trust him fully and instructed his political ally Lazar Kaganovich to become friends with Yakir and to report about his activities.
Split into simpler sentences: Stalin, who was consolidating his power over the country, approved Yakir's appointment to the Ukrainian Military District in 1925. However, he did not trust him fully and instructed his political ally Lazar Kaganovich to become friends with Yakir and to report about his activities.