Before the introduction of the eighth plan, the United States and Britain had negotiated seven plans, but all of them were rejected, mainly because the people who made the plans were British politicians. Obviously, the credit for the war cannot be exclusively enjoyed by Britain, but must be formulated by the United States. After the introduction of the eighth plan, Montgomery felt that it was too risky to go ashore from Sicily and then defeat the Axis countries in all directions, and the strength of each army would be greatly weakened, which would probably lead to heavy losses for the US military.

This scheme is also extremely risky. If the opponent defends a landing port, many areas will be breached one by one. Secondly, in the plan made by Britain, most British troops can directly control big cities, while the places attacked by the United States are some nameless towns. This led the United States to be very dissatisfied with Britain's strategy, because it ignored the control of the United States and put the United States in a passive position, only getting a little benefit and not taking the main credit, so Montgomery also disagreed with the eighth plan. On the other hand, this landing plan puts the United States in a state of being bashed head-on, and will certainly bear the greatest risk.

The us military has just arrived in the Mediterranean region and lacks understanding and experience in the battlefield.

The region where the United States and Britain are located is in the Mediterranean Sea, which makes it difficult for American soldiers on the other side of the Atlantic to adapt to the climate in this region. Secondly, the United States and Britain are in a passive position in this war and need to take the initiative to attack. However, when the US military first arrived in this area, many soldiers were not adapted to the climate and did not know much about the operational situation and geographical conditions in this area.

So Montgomery wanted to wait until all the soldiers recovered their energy, and then made a detailed battle plan, and then organized the soldiers to attack after understanding the local geographical situation. Later, he also wanted to give the US military more time to conduct field exercises, especially the comprehensive amphibious landing exercise.

Lack of strength, plus the battle between Montgomery and Barton.

In the Battle of Sisi Island, the US military had only 300,000 troops, which was far from enough to win. And Barton and Montgomery have always been sworn enemies, and the plan was rejected because of the confrontation between Montgomery and Barton.