Zambia presidential election results are in at about half of the country's constituencies. The Patriotic Front's Michael Sata has an early lead over incumbent Rupiah Banda, whose party has been in power for 20 years, but it is much too early to call the election.

With 85 of 150 voting districts tallied, Sata leads the race with 43 percent of the vote, compared to President Banda's 36 percent. However, Banda still leads in the most recent opinion polls.

The two politicians fought a fierce battle in the 2008 presidential elections, with Banda edging out his nationalist opponent by a mere two percentage points. Sata alleged that the vote has been tampered with, a claim that has again arisen in this year's vote.

The general election was held on Tuesday, and the slow pace of vote counting has angered many Zambians. There were protests and riots in a number of copper mining towns, as well as in the slums of the capital of Lusaka.

Sata's base is primarily the working class and impoverished, while Banda is a pro-business president. Many Sata supporters are the copper miners who sustain Zambia's largest and richest industry.

Many lower-class Zambians are upset over a 2007 investment deal with China that created an economic partnership zone on a large copper mine. The deal was beneficial to Zambia's economy -- China is the third-biggest importer of Zambia products -- but the average Zambian felt left out, and the jobs promised by Banda have been slow to come.

Banda's political party, the Movement for Multi-party Democracy, has held power since 1991, winning each election since the country abandoned the single-party system.

After Zambia gained its independence from Great Britain in 1964, the country became a democratic republic. Once President Kenneth David Kaunda came to power, the country remained a one-party system for three decades. Enjoying near-immunity from losing his seat, Kaunda served as President until 1991, when riots, demonstrations and an attempted coup forced Kaunda to create a multi-party democracy.

In the past few years, China has begun an aggressive economic push into Africa. Along with Zambia, China has ventures in iron-producing Gabon, and has significant oil deals in Angola and Sudan, which sells about two-thirds of its petroleum to China. In fact, there are few African countries where China hasn't made at least a small investment.