The United States remains weak economically, but outside our borders, prosperity has returned. Economist Ed Yardeni calls this phenomenon "the Greatest Global Boom of All Time," a theme he and other world-wide bulls have embraced as emerging economies emerge further. The next year should prove pivotal to that investment thesis, as the rising economic tide that's lifted most boats abroad starts to break up and offer choppier seas. Many factors will make waves, including the pace of a U.S. recovery, the strength or weakness of the dollar, political stability in emerging markets and the trajectory of energy and commodity prices. It's a complicated picture that changes with alarming speed, as was the case with sudden recent crises in Greece and Dubai. Here are a few national economies to keep an eye on in 2010 as the gears turn smoothly in some places and grind hard in others.

Major stock indexes, 2009 performance:
SSE Shanghai Composite: 75.2%
Shenzhen Stock Exchange 100 Index: 111.4%

Apart from the United States, this is the country to watch in 2010. China is the leader of the BRIC bloc of formidable emerging economies, which include Brazil, Russia and India. China is our economic frenemy, a trading partner and rival, the holder of $800 billion of our debt. It's also in the midst of another rapid growth spurt fueled by government stimulus spending, rising consumer spending and heavy use of commodities. It's a classic financial bubble, and it will pop. The questions investors raise are: When, how hard and how on top of the market economy is the Chinese Communist Party? Chinese demand drives up commodity prices, and a chaotic economic collapse could really stir up some dust.

Brazil

Major stock index, 2009 performance:
Bovespa: 34.2%

The wags used to say that "Brazil is the country of the future, and always will be." The future's here. Brazil is a leading commodity exporter and a pretty sizable consumer, as well. Its economy is diversifying, as its banking sector and domestic consumption grow and mature, but they are both potential weak links. Robust trade in commodities is helped by a weak dollar, and signs that our currency is on the upswing may affect Brazil's full-tilt growth rate.

Russia

Major stock indexes, 2009 performance:
RTS Index: 124.8%
Moscow Interbank Currency Exchange (MICEX) Index: 110.5%

Russia is a classic party crasher: rich, but a bit unstable and prone to gaffes in polite society. Its vast wealth of natural resources, from oil and gas to the timber of the taiga, make it a major player on the world stage. American investors have flocked there along with European money in hopes of getting some profitable order established, but its deeply entrenched culture of crime and corruption close to its political elites makes this unlikely in the near term. As a resource economy, Russia is subject to the same vicissitudes as Brazil, but its shaky legal and regulatory framework make the nation a riskier bet.

India

Major stock index, 2009 performance:
BSE Sensex: 82.5%

India isn't quite a continent, but it's nearly one, and so it goes with its economy. It isn't quite self-contained, but it's such a massive entity with so much of its energy directed toward internal growth and a gradual leveling of tremendous inequalities that it's not quite as vulnerable as the other BRICs. Much of its industrial output is for domestic consumption, though that is changing slowly. As the hangover from its nationalized economic heritage is shaken off, India should see significant export growth. It's already gotten a big share of outsourcing jobs in the information technology sector, and as long as Indian labor remains cheap and English-speaking, that should provide some consistent profit.

The United Kingdom

Major stock index, 2009 performance:
FTSE: 23.8%

Our sixth-largest largest trading partner has had a pretty rough year, in no small part because we've made many of the same mistakes. Housing bubbles, banking busts and an urgent need for government money and oversight to arrest its economic slide have all made British headlines in 2009. Digging out from under will take time, and may prompt a change in political leadership when the U.K. holds its general election in June.

South Africa

Major stock index, 2009 performance:
JSE Top 40: 64%

The world's eyes will focus intently on Africa's most prosperous, but still problematic economy, as fans cheer on the World Cup competitors in matches across South Africa, culminating with the final in a Cape Town stadium completed earlier this month. South Africa's economy was built on gold, and while it has diversified significantly look for cheap, high-quality wines from the Western Cape at your local liquor store it's still a struggling country with many challenges. Hosting a global soccer tournament isn't the country s only goal in 2010, but it should help boost South Africa's level of play.

Germany

Major stock index, 2009 performance:
DAX: 25.0%

The strongest economy in Europe has assumed even greater importance as its partners in the 16-member eurozone region appear weaker. Earlier this month, the research institute Ifo reported German business confidence rose to its highest level in 15 months. That's good, because it's going to have to run with the recovery ball for a while. The French national statistics office Insee reported weakening sentiment, and the well-publicized problems of Greece and Ireland point to an uneven outlook and economic prospects that could widen fissures in the currency union.

Japan

Major stock index, 2009 performance:
Nikkei 225: 18.9%
Topix: -26.6%

The world's second-largest economy, and our fourth-biggest trading partner, keeps looking like it's strong enough to get out of its decade-long sickbed, but then it relapses anew. The days of Japan Inc. functioning as a well oiled corporate machine are pretty much done, but 2010 could be a better year for the country, albeit one in which more modest expectations are in order.

Canada

Major stock index, 2009 performance:
S&P/TSX composite index: 35.5%

Our northern neighbor is riding its natural resources to a robust 2009 finish, despite some volatile fluctuations in the global commodities market. During this period of unexpected role reversal with our biggest trading partner (something we often overlook down south), the Canadian dollar has strengthened and that's got some market watchers worried that the country is being set up for a bit of a bubble pop itself.

United Arab Emirates

Major stock indexes, 2009 performance:
Dubai Financial Market (DFM): 12.6%
Abu Dhabi Securities Exchange (ADX): 16.9%

The recent debt crisis in Dubai threw this vital part of the world into sharp focus early this month. This federation of Gulf States is an anchor of relative stability in the Middle East, serving as a financial center, a hub for energy-related activity and of course, a sinkhole of expensively financed real estate overbuilding. As it sorts out its financial housekeeping, investors can draw a lesson from the crisis the appearance of prosperity doesn't mean there's substance behind it.