Which disadvantages for a region if the rest of the world doesnt recognize it?

[bytebuster]

Q: Which disadvantages for a region does it have declaring the independence from its country if the rest of the world doesnt recognize it?  // Ну як діти малі, чесне слово, усе доводиться їм розжовувати. :-) Але приємно, що Accepted answer через хвилину після написання, я навіть не всю граматику вичитав, а ОП вже прийняв. Приємно.
І ти тоже, %USERNAME%, піди хоч плюсіка мені постав за відповідь, не будь жадіною! :-)

Today Catalonia declared the independence from Spain.

The European Union and United States stated they only will treat with Spain, meaning they do not recognize Catalonia as a country.

Which disadvantages does this have aside they can't negociate directly with the United States and countries of the European Union? How does this affect for example, exports and imports from United States and the European Union to the region of Catalonia?

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A:

TL;DR: The lack of recognition leads to a "corruption tax" paid by the citizens of an unrecognized territory. That's why the recognition is the key factor for any region.

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Consider this (the US is just for example below):

Politically, the US is an ally of Spain, and many international treaties recognize the territorial integrity of Spain, in its existing borders. Hence, the US will not co-operate with any entity that undermines this integrity.

Economically, imagine that an US exporter/importer signs a deal with a company based in the independent Catalonia. A legal Spanish competitor would seek justice and be able to win the case in the court.

So, the direct answer to your question,

How does this affect for example, exports and imports from United States and the European Union to the region of Catalonia?

— There will be zero direct exports and imports in this case.

However, there will be indirect trade, just the way how ISIS trades oil via the corrupted proxies located in recognized countries. Most obviously, such trade assumes significant discounts (also called "corruption tax", CT).
In other words, if a recognized entity sells something for $1, an unrecognized one would be able to sell the same good for $1-CT so that, after being "legalized" through a chain of corrupted proxies who take CT as a premium, the item could be legally sold for $1.
The same applies to import: an unrecognized entity would be able to buy something for $1+CT.

So, the people who live in an unrecognized country, will suffer by paying the corruption tax twice: both for import and export. This is the main disadvantage.

A country can also rely on its own resources. For instance, Juche, the official state ideology of North Korea, is based on self-sustenance, relying solely on its own resources, and denying the international trade.