Every period has its own foreign policy challenges.
1900-1914:
Challenge for the European power to keep the extremely successful peaceful co-existence - unsuccessful
1918-1928:
Challenge to re-arrange the peaceful co-existence - preliminary success, but evil seeds were sown both in the treatment of Germany, the interventions in Russian civil war and by giving up the close relationship between UK and Japan.
1929-1935:
Challenge to master the World-wide economic crisis - an economic science learning process
1936-1941:
Challenge to master the rise in power and limit the expansion of Germany, Soviet Union and Imperial Japan - total failure
1945-1950:
Challenge to re-arrange the global relations between powers, especially in Europe and in regard to the Soviet Union - failure
1951-1990:
Challenge to prevent a hot World War III as minimum requirement - successful
1991-2000:
Challenge to re-arrange global relations because of the Warsaw Pact falling apart - initially promising, but apparently moved on a wrong track with the 1999 Kosovo Air War.
2001-2007:
Challenge to master the relatively tiny problem of AQ terrorism (remember; few years ago, it was about not exterminating mankind!) and challenge to re-arrange the West's relations to Russia and PR China - the reaction to terrorism was apparently a huge and wasteful over-reaction that created new troubles. The relations to PR China seem to be either simple "business as usual" or not really defined yet. The relations with Russia didn't improve, and Russia's partial recovery led to the first hot clash "West" vs. Russia, which was on first sight won by Russia.
What will be the challenges for the future?
I see five hot topics.
A) Russia
Russia's "place in the world" needs to be defined again (mostly by itself).
Russia's role as important country in the global economy, in the short term especially concerning the raw materials supply.
The background is very complicated because of Russia's past as superpower, traditional dominance over its neighbours and a residue of Pan-Slavism.
B) PR China
The China situation is very similar to the one about Russia.
China's "place in the world" needs to be defined - the Chinese are apparently interested in their pre-19th century regional dominance and secured sea lanes for trade.
China's role in the global economy needs to be defined; its trade surplus isn't sustainable, and a growing trade surplus isn't even sustainable in the short term. China needs to transform itself into a nation with strong domestic consumption, but at the same time it needs to limit its disadvantageous impact on global raw material supply and global climate.
The background is very complicated because the regional dominance is so far a U.S. dominance, and all three regional powers (China, Korea, Japan) would like to see their position improved - a win-win seems to be impossible.
The much worse background-related problem is the repeated humiliation of China by European powers, the USA and Japan till the late 1940's.
C) India
India is a bit behind China in its economic development and is a very different country.
It needs a secure overseas trade, has a conflict with Pakistan looming about Kashmir, has some domestic terrorism troubles, the Sri Lanka civil war next door, Myanmar with its problems at the other next door and is a nuclear power.
Its economy is becoming an important factor in the global economy and needs to become sustainable (economic balances, climate, raw materials demand).
The historical background is again difficult; the caste system is still influential and it has a history as colony of European powers (England mostly).
Maybe the 'Western' states in the Commonwealth are in the best position to address frictions that will happen between the 'Western' nations and India.
D) Terrorism and Pakistan
This mess has only grown since 2001 in my opinion.
The challenge is simple; keep Pakistan from using its nukes.
This is really a good opportunity to accept that international affairs are difficult and that it could be wise to accept even a deterioration in order to avoid the worst case.
The challenges of our time are visible - will they be addressed properly?
S O