This is mostly false. I'll try to explain.I don't believe it is false. Instead of explaining again, can you provide specific verifiable assertions and citations? I'll make it easy, I'll give you specifics to refute.
If subsidization of farmers to produce more than the market is predicted to demand in order to smooth out volatility and prevent famine is necessary (and it seems to me like a laudable goal), government can simply fund overseas farmers to overproduce, rather than its own. It would be less expensive than the current process in those cases where overseas farmers produce more cheaply. In many cases they'd still be subsidizing their own farmers.
Is your argument truly based on the assumption that government generally solve problems in efficient ways??
The truth is that it is easier for most governments to justify giving subsidies to their own citizens rather than foreign countries. Also self-sufficiency on food is seen by many as a security issue, and therefore there is a resistance to relying on others.
That said, different countries use different solutions. See http://www.guardian.co.uk/global-development/2012/may/10/chi... for a news article indicating that China is taking exactly the efficient approach that you suggest.
Pretty much the only thing that would be untenable would be the current practice of paying "farmers" who own land to not produce. As far as I can tell everyone who doesn't receive that money hates the practice, so maybe we should just stop doing it. Which brings me to...
The USA pays people to keep land ready but unused so that production can rapidly improve. The European Union instead accumulates surpluses - aka the famous "butter mountains" and "milk lakes". Those are just different means to the same end - ensuring that there won't be a major famine.
> After repeated bad experiences, every country with the capability has decided that they want farmers to grow extra in normal years.
They haven't really. It's not like we ever had a vote on it. The current process is just a powerful lobby exercising their considerable power.
No, YOU never got to vote on it. It was before your time. That doesn't mean that I am wrong.
The European Union's policies were explicitly adopted as a reaction to famines after WW II. (Which in turn were significantly lessened thanks to major US intervention.) See http://en.wikipedia.org/wiki/Common_Agricultural_Policy for confirmation.
The US policies started earlier, and were motivated by the Dust Bowl in the 1930s. http://stateimpact.npr.org/oklahoma/2012/11/16/ken-burns-dus... is one of the first links that I came to which can verify that.