Markets across the world may have risen to record highs in 2013's run-up, but the great gains made by investors, companies, and leading economies haven't extended around the entire globe. Many parts of the world still struggle with rampant poverty and myriad other economic problems. But just which nations make up the unfortunate group of the five poorest countries in the world?

Earlier in the year, we looked at the five richest countries in the world, with a few names on the list that may have surprised some. Now, using projected 2013 per capita GDP figures from the International Monetary Fund and adjusted for purchasing power parity, let's start off with No. 5 on the list of the world economies most in need.

5: Liberia, $710 GDP per capita
Liberia's been hit hard by instability and conflict in the past, but it's a nation that's clinging to hope for a better future. The West African country of only a little more than 4 million people suffered through years of civil war before a 2003 peace accord brought an end to the fighting and ushered in a new wave of cautious, but promising, democracy. Liberia's history of violence has left its scars on the country's fragile economy, as considerably morethan half of all Liberian citizens live below the poverty line. However, like other notable developing economies, Liberia's rising up behind a familiar sector: energy.

Monrovia, Liberia. Source: Wikimedia Commons.

Energy exploration firm African Petroleum unearthed significant oil deposits off Liberia's coast in early 2012, and leading energy firms have been quick to move in. China's been a particularly active player in African economics in recent years, and state-owned oil firm PetroChina (PTR) added to Beijing's moves by inking a deal in July of last year to invest in up to a 20% stake of one of African Petroleum's Liberian oil blocks. Despite PetroChina's precipitous stock fall this year, the company's been making major moves in West Africa.

American firms haven't been left behind in Liberia's oil rush, either: ExxonMobil (XOM 1.15%) acquired an 80% stake in a Liberian offshore oil block just this May through one of its subsidiaries. ExxonMobil's followed other international energy giants into the region, and its entrance into Liberia's energy market -- along with that of PetroChina and other top global players -- should only help this rebuilding economy take its early steps in rebuilding from years of conflict.

4: Eritrea, $705 GDP per capita
War-torn East African Eritrea has had its share of violence just like Liberia, but unlike the fifth-ranked member on our list, only rumors about Eritrea's natural resources have sprung up. Major energy and materials companies haven't moved into this country, which saw its economy slugged by war with neighboring Ethiopia to start the millennium. It hasn't gotten much better for the Eritrean people since, as allegations of government corruption and abuse have turned the country into a top global producer of fleeing refugees, according to United Nations investigations.

Unlike Liberia, the situation here isn't likely to get much better fast -- for either Eritreans or global companies with African ambitions, such as aforementioned ExxonMobil and PetroChina. With Eritrea's oil and energy situation a virtual unknown and little in the way of economic or political stability, this is a country stuck in a rut. The IMF estimates that Eritrea's per-capita GDP adjusted for purchasing power parity will grow only around 1.7% between 2013 and 2018, a mark that will lead to the nation being ranked as the second-poorest country in the world by that time.

3: Burundi, $640 GDP per capita
Landlocked Burundi in Central Africa is facing far more struggles than it can overcome quickly. According to the World Bank, this nation of nearly 9 million people saw more than two-thirds of its population living below the poverty line as recently as 2006. While this middling economy's picking up steam -- the IMF estimates Burundi's economy will grow by 25% between 2013 and 2018 -- it's hardly an attractive target for major multinational corporations.

Burundi's attempting to make headway in that department by recently agreeing with several other neighboring nations on adopting a common currency in the near future, but it has plenty more challenges to overcome. Corruption and unskilled labor plague Burundi's attempts to improve its economic position, and foreign investment only now is starting to trickle into the economy's coffers. The country ranks as one of the worst business environments in the world, and until that improves meaningfully, major multinational firms -- and investors -- will see little attractiveness out of this struggling economy.

2: Zimbabwe, $571 GDP per capita
Zimbabwe's economy imploded thanks in part to the country's infamous collapse of its currency. Hyperinflation plagued Zimbabwe and reached insane annual growth heights in the sextillion percent range, forcing the nation to fall back to relying on the U.S. dollar in the past few years as its primary currency. Still, the nation suffers from numerous major social and economic troubles, including more than seven in 10 Zimbabwe citizens living beneath the poverty line as of 2011, according to the World Bank, and a 95% unemploymentrate as recently as 2009.

Zimbabwe 100,000-dollar note. Source: Wikimedia Commons.

Those aren't good conditions for top international corporations to take advantage of. Zimbabwe does have some advantages -- the population's highly literate, much more so than many other developing African countries, and the nation's home to sizable reserves of minerals such as platinum and gold -- but a poor political situation under the three-decade rule of President Robert Mugabe, along with other factors, has led to sanctions from leading Western nations. Zimbabwe's nowhere near an even tolerable business climate, and only China's investment has marked major international participation in this floundering economy.

1: Democratic Republic of the Congo, $386 GDP per capita
The world's poorest nation has one thing going for it: It's huge. Congo's among the 20 most populous nations in the world, but severe problems have prevented the country from realizing anything close to a stable economy. The M23 insurgent group has been the latest blow to the DRC's hopes, and the two sides only signed a peaceagreement to end the rebellion formerly on Dec. 12 of this year. Further civil wars plagued the DRC from the end of last century into the early years of this one.

Until Congo realizes some semblance of stability, it won't be able to even see hope for its struggling economy. The IMF projects strong growth from the Congolese economy going forward, but the nation's per capita GDP figure is so bad that such growth would still make the IMF's projection of the DRC's 2018 per capita GDP rank as this year's poorest economy as well.

It's a shame, as Congo's ripe with raw materials. The country's a major producer of tungsten and gold, among other minerals, and the DRC's total resource wealth is estimated at up to $24 trillion. International corporations haven't shied away from this conflict zone: Major miner Freeport-McMoRan (FCX -1.10%) operates both copper and cobalt projects in Congo, and it's only one of numerous multinational firms getting involved in the country's resource wealth. Freeport-McMoRan's dealt with its share of problems particular to such a weak economy, as the firm's pulled back on operating rates at its Congolese mines in past years due to power outages. However, while Congo's population might not be reaping the wealth of its natural resources just yet, this country's vast mineral wealth has the potential to make miners like Freeport-McMoRan and its rivals – as well as their investors – very happy indeed.

How can an investor benefit?
One thing's clear about all of the five poorest countries in the world: There's no easy way for investors to take advantage of these nations' economies. Even countries with potential, such as the DRC and Liberia, struggle with political, social, and economic woes that won't be going away soon and present huge obstacles for international corporations.

However, resource companies in both the materials and energy sectors have wizened up to Africa's potential over the past decades. Companies such as Freeport and Exxon-Mobil, among others, face great potential if they can take advantage of Africa's mineral and resource wealth, and China's made a strong push into Africa in its own bid to secure natural resource dominance. Investors shouldn't ignore this struggling, but potential-laced, area of the world: Some of the poorest countries on Earth have the resource potential to make your favorite companies and stocks rich.