I just learned from this question that Germany is storing its gold reserves around the globe.
Why would a country store any of its gold reserves abroad, instead of well-protected inside the country? When did Germany create those exported deposits?
And an optional speculative question: what political goals could be driving the request to fetch the gold back?
According to Der Spiegel, part of the reason why it is stored in the USA may be because a bunch of that gold was purchased from the USA.
Before the gold standard was terminated in 1971, the current account surpluses generated by Germany's "economic miracle" were partially balanced out in gold. Thousands of US bars of gold alone were transferred to German ownership.
Securely moving tonnes of highly valuable metal intercontinentally is a non-trivial endeavour, and once it got to Germany, they'd need to deal with storing it, so they presumably decided to just leave it where it was with a "Eigentum der Bundesrepublik Deutschland" label on it rather than deal with that hassle and expense.
Remember that from 1949 till 1989 West Germany lived under the threat of a Soviet invasion; Frankfurt/Main was supposed to be the first target of the Soviet army (see Fulda gap). So storing most of the gold reserves where the enemy could not get them easily (i.e. London and New York) made sense.
In continental Europe, safety was a primary concern as Martin Schröder explained. For Germany, having gold on another continent is a way to make sure it could not easily fall in the hands of the Soviet Union.
But there are a few other good reasons to continue to store it abroad today. Compro01 mentioned the fact that some of this gold was probably purchased in the US and it would be very complicated to transport it back to Germany. But for gold stored in Germany, you would have the exact same problem when you want to sell it. So it makes more sense to keep gold close to where it can be bought and sold.
Finally, secure storage facilities do cost money. Even if you have to pay some foreign country for storage (traditionally it was not necessary but some countries now charge for it), it might still be cheaper than creating or enlarging your own vaults.
Note that this is mostly a hangover from past times. In spite of regular populists call to “keep our gold” in Germany, the real question is why bother with holding gold in the first place? Countries are mostly stuck with it for historical and emotional reasons and can't even offload it easily. The UK has actually tried to get rid of some of its gold some years ago, tanking the price in the process.
All the answers so far have assumed that once a country buys gold, they never sell it. Central banks do buy gold when it has a low cost in their currency and sell it when it has a high cost in their currency. Switzerland, London and New York are centers for gold trading (there are other places) and the banks save money by buying the gold on, say, the London market, leaving it in London, then selling it to, say, Japan in the London market and not transporting it around the globe. There is also a practice of lending out gold and being repaid in gold and the interest is also paid in a specific agreed amount of gold.
I think it's not just historical reasons that most mentioned in the above answers. Most trade chains involve a large number of countries from all over the world. Gold or steady currency (dollar) is the most convenient way to settle accounts. Gold is expensive and heavy, and its transportation is inconvenient for world trade. The international gold market is changing rapidly. If a country is in urgent need of foreign exchange, it's uncertain to transport how much gold for trading. Therefore, for most countries, the easiest way is to store gold in the U.S... When it needs to pay a trade, it exchanges dollars through gold. Others who get dollars in the trade, can exchange gold through these dollars if they have too many dollars. However, the gold could be still stored in the U.S... After all, nobody knows how many dollars will be needed in another sudden trade, which is also a sudden opportunity can’t miss.
As for why Germany wants to take back gold. According to the situation at that time, I have no idea. But one thing is sure that if the U.S. refuses to permit Germany to examine its own gold, it will cause concern. And as we can see in these years, the US dollar's supreme position is also potentially challenged by RMB. The credibility of the dollar has relatively fallen in some slight degree in recent months.
