Answer: The phrase "dissuaded from so strong a statement" means that someone has been convinced or persuaded to not make a very forceful or definite statement. In other words, the person has been persuaded to soften their language or tone when expressing a particular idea or opinion.
For example, if someone is planning to make a statement that is very critical or controversial, they may be dissuaded from doing so by someone who advises them to be more cautious or less forceful in their language. The phrase implies that the person has been convinced to reconsider their position and perhaps express it in a more tempered way.
Explanation: In this context, "dissuaded from so strong a statement" means that the president was initially planning to make a very forceful statement, but someone convinced him to tone down his language and choose a less strong statement instead. The passage suggests that the president was originally planning to make a statement that outright rejected Pétain's assurances of adhering to the 1940 armistice, but was dissuaded from doing so by someone, perhaps to avoid escalating tensions or risking a negative reaction. Instead, the president chose to warn the French people about the potential threat of Franco-German collaboration and appeal to them to reject the Axis powers.