The letter signed by Samuel Adams caused very negative reactions in the British, which increased tensions between the British Parliament and Massachusetts, who not to give up what the letter said, led the British Empire to decide the occupation of the city of Boston by the British Army. This fact, in turn, and given the repressive forms of reaction of the British, was a fact that rushed and provoked the American Revolution. It should be noted that in the letter, it was expressed at the end that the settlers were still subjects of His Majesty and that only expressed with anguish their problems.
The main aggressor during WWl is considered to be Germany.
You will have to look at whether or not the creator of the source had a really positive or negative outlook on the situation.
If they are -for example- great friends with a bully, they will not tell as much of the truth, but if they are enemies, they may tell a very exaggerated truth to get them in trouble.
You must look for a very neutral feeling on both sides of the matter. If the author has an opinion, more likely than not it will affect the way they share the information