"Complete takeover" means to gain full control or authority over something or someone, usually by overpowering or replacing them entirely. Full definition
What is involved in completing the takeover of a football club? (footballwhispers.com)
The approach resulted in a nearly complete takeover of the recipient's immune system by the donor's immune cells. (sciencemag.org)
Yonghong Li completed his takeover of AC Milan on Thursday, and is expected to address the media in a press conference on Friday to outline his plans. (caughtoffside.com)