Aviation Week is reporting that EADS-North America felt it needed an partner on the KC-X contract as it was not comfortable being the prime for such a large effort. While EADS has experienced some decent growth in the U.S. it still has a fairly lean organization.
The company was confident that they could provide to Northrop the basic airframes on cost and schedule. Northrop would have then been responsible for the necessary military modifications. EADS would have had to find a partner in General Dynamics, Raytheon or Lockheed Martin. There would be few large contractors available in the U.S. with the past experience to support a contract of this size.