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When you say investing in a country, I think you mean investing in the real sector.
Investing in a country provides the creation of new jobs. If unemployment decreases, workers' wages improve because it becomes harder to find workers. Also, more production facilities means more competition. If there is competition somewhere, the prices of the products will also be cheap. Additionally, new investments mean new tax revenues for governments. In short, investing in the real sector is beneficial for people and states.
From the way I understand my own way of investment in a country. I saw it like something that we help the country to increase their economy because any country who invest anything in order to support and boost the country source of getting money or generating income is not way of reducing unemployment because investment is different from unemployment it is when your investment or matured is when you will talk of reducing unemployment.