Why is this sentence awkward?

Activate doesn't make sense in this context. The economy was activated centuries ago. It was never deactivated. It's just the wrong verb for this context.

I think activate would be why. An economy is always active, so I think a better word for the idea this sentence seems to be trying to convey would be stimulate, which convey that the tariffs were intended to increase existing activity. In reality though, I think another reason this sentence is awkward is because -as far as I understand- the idea it is trying to convey isn’t quite correct. The (claimed) reason Trump imposed tariffs was to stimulate domestic production and industry. Domestic production and industry is fundamentally different from the country’s economy as a whole, as the economy as a whole encompasses ALL economic activities of an entity, including consumption, which would include imports.

Who said it's awkward?

I think the "was" is confusing. A simpler version of the same sentence would be, "Trump imposed tariffs to activate the country’s economy."

Does it help if we add the missing "that"? The reason that Trump imposed....

It's not particularly awkward, but it may not convey the intended meaning. In particular, things do not "activate" the economy, they "stimulate" it. That's not awkward, it's a usage problem. There are different ways to express this depending on what you want to emphasize. You want to emphasize that this is Trump's intent, but may not be reality: *Trump said that he imposed tariffs to stimulate the country's economy.* You are doing your own analysis and concluded that this was Trump's intent: *Trump imposed tariffs to stimulate the country's economy.* Using "The reason...was" is not awkward but it's deadwood. They are extra words that add nothing to the meaning. The phrase "to stimulate...." is self-evidently a reason. (I am tempted to reword this to the factually correct version but I assume that politics would not be welcome here.)

It's unclear what activating an economy means, as an economy is already active.

i don't really think it's awkward

Apart from the odd use of "activate" that other people are commenting on\* , you could simplify the sentence to "Trump imposed tariffs in order to activate the country's economy" or "Trump imposed tariffs, and the reason was to activate the country's economy". Either way it avoids splitting up the subject ("reason") and the verb ("was"). To me that's the most awkward thing about the sentence. *\*I don't think it's that bad, it's obvious what is meant and implies that the economy was stagnant but is now being "activated". I think that's mostly people being kind of pedantic about other people's language.*

Grammatically or economically speaking ???

It reads fine to me. https://www.merriam-webster.com/dictionary/activate I guess some people being overly pedantic could argue that “activate” isn’t the best word in this context, but Webster’s dictionary seems to include things becoming more active in the word’s definition and it doesn’t seem like the wording would be out of place in something more formal like a news editorial.

'activate' it not collocated with 'economy'. 'economy' is collocated with 'grow', 'collapse', 'recover', 'stabilize', 'boost' and 'stimulate'. These are the verbs you can most commonly use with 'economy'.

It is completely fine to me. (Other than it (probably) being false)

Sounds fine to me, maybe something about “the reason… was *to* _” doesn’t sound perfect (specifically the word to) but I don’t know how else I would phrase it

It's unnecessarily verbose. > Trump imposed tariffs to activate the country’s economy.