If "eng mit" means "closely related," why would it be necessary to add the verb "zusammenhängen?"

Question

Occasionally I spend time with Duolingo's Immersion feature, which allows users to try their hand at translating any number of documents. The other night I submitted a translation for a sentence that two other users had already submitted translations for. Both of them added a word to the translation that didn't seem necessary to me, but since I am not fluent in German, I've been wondering if it might be necessary after all. Below I have listed the English sentence followed by the three translations. The word that seems unnecessary to me has been bolded:

It* deals with economic warfare such as the blockade of Germany, and with some issues closely related to the economy, such as military issues of transportation.

Translation #1:

Sie befasst sich mit dem Wirtschaftskrieg wie die Blockade Deutschlands und mit einigen Problemen, die eng mit der Wirtschaft zusammenhängen wie militärische Transportfragen.

Translation #2:

Sie befasst sich mit dem Wirtschaftskrieg wie die Blockade Deutschlands, und mit einigen Problemen, die eng mit der Wirtschaft zusammenhängen wie militärische Ausgaben des Transportes.

Translation #3 (my translation):

Sie befasst sich mit dem Wirtschaftskrieg wie die Blockade von Deutschland und mit einigen Problemen die eng mit der Wirtschaft wie militärischen Fragen des Transportes.

*"It" refers to "the economic history of World War I."

Up until recently, I've been limiting myself to just the translation of words and short phrases, but want to start challenging myself a bit more with full sentences. Seeing translations that don't quite make sense to me question my ability to do a decent job of it.

I actually attempted to contact one of the other translators, but have not received any word back, so I thought I'd present this here to see if anybody in this community can explain why these other translators added the word zusammenhängen.

Answer 1

In the English sentence, the subordinate clause

and with some issues closely related to the economy

uses an adverb and participle construction to express the closeness. You could also maintain the view that the the verb has been omitted and the phrase would then be:

and with some issues that are closely related to the economy

In the German translation another route has been chosen, with a verb construction in the present tense mit [etwas] eng zusammenhängen, which is a fixed phrase, and you simply need the zusammenhängen. Your last example is not possible; you need to have a verb in this subordinate clause. Eng mit [etwas] sein is another construction with the use of eng mit, but still you need a verb.

Another translation, without a verb, may be closer to the original, but less idiomatic German would perhaps be:

Sie befasst sich mit dem Wirtschaftskrieg, wie der Blockade Deutschlands und mit einigen Problemen mit engen Beziehungen zur Wirtschaft, wie Militärtransportfragen.

Answer 2

Translation #1 is the best one. You definitely need zusammenhängen, #3 misses a verb. Also I would replace Problemen with Themen. Issues is a very mighty noun, it can be translated to Probleme, Themen, Tatsachen, etc.

Answer 3

"Eng mit" would be more like "close to", as "eng mit" does not contain a verb