A trader works at his post on the floor of the New York Stock Exchange (NYSE) in New York. Brendan McDermid | Reuters

Major stock markets across the world suffered their worst calendar year since the financial crisis in 2018, leaving many global investors fearful of further declines over the coming months. Simmering trade tensions between the world's two largest economies, growing concerns over rising interest rates and persistent geopolitical issues — such as Brexit — battered financial markets last year. But, there were some notable exceptions to the general doom and gloom over the past 12 months. CNBC takes a look at some of the best and worst performing global stock market indexes in U.S. dollar denominated terms for 2018.

Ukraine +80.39%

Ukrainian soldier stands guard aboard military boat called 'Dondass' moored in Mariupol, Sea of Azov port on November 27, 2018. - Three Ukrainian navy vessels were seized off the coast of Crimea by Russian forces, which fired on and boarded Kiev's ships after several tense hours of confrontation. Here's what is known about Sunday's incident. SEGA VOLSKII | AFP | Getty Images

Ukraine's stock market index (PFTS) skyrocketed more than 80 percent in 2018, according to data sourced from Refinitv, comfortably becoming the top performer worldwide. This rise came despite Ukraine's request for help from its international partners at the EU and NATO after Russia seized three naval vessels and 23 crew members in late November. The incident happened in the Kerch Strait, a channel that separates the Sea of Azov and Black Sea, to the south of Ukraine and Russia.

Macedonia +30.41%

People wave Macedonian flags during a protest in front of the Government building in Skopje on June 2, 2018. ROBERT ATANASOVSKI/AFP/Getty Images

The blue-chip MBI 10 index of the Macedonian Stock Exchange (MSE) rose almost a third in 2018. It comes after the country reached a breakthrough agreement with Greece to settle a long-running name dispute. Skopje agreed to change its country name to Republic of North Macedonia in June, effectively ending perceptions by some that it held territorial claims to the Greek province of Macedonia. The move must still be ratified by both Macedonian and Greek parliaments.

Qatar +20.87%

Three Arab women wearing traditional abaya watching the futuristic skyline of Doha, Qatar. Buena Vista Images | DigitalVision | Getty Images

Qatar's stock exchange surged over 20 percent in U.S. dollar denominated terms in 2018. The small Gulf state officially left OPEC on Tuesday, ending a membership which had stood for more than half-a-century. Doha announced it would leave the Middle East denominated group shortly before a critical meeting between the influential oil cartel and its allies in December. Since June 2017, OPEC kingpin Saudi Arabia — along with three other Arab states — has cut trade and transport ties with Qatar, accusing the country of supporting terrorism and its regional rival Iran. Qatar denies the claims, saying the boycott hampers its national sovereignty.

UAE +11.75%

The Burj Al Arab with the flag of the United Arab Emirates in Dubai, UAE. Thomas Janisch | Getty Images

The United Arab Emirates' ADX General Index rose nearly 12 percent in 2018. UAE Economy Minister Sultan bin Saeed al-Mansuri told reporters in early December that he expects the Arab world's second-largest economy to grow between 2.5 percent and 3 percent in 2019. The projections are in line with the International Monetary Fund's (IMF) forecast.

Saudi Arabia +8.77%

Crown Prince of Saudi Arabia Mohammad bin Salman speaks in Riyadh. Bandar Algalour | Saudi Kingdom Council | Anadolu Agency | Getty Images

Saudi Arabia's stock market plunged as global investors fretted about deteriorating relations with the international community in 2018. The kingdom's royal family has endured three months of intense scrutiny after Saudi agents killed and dismembered Washington Post columnist Jamal Khashoggi in Istanbul in October. The incident has drawn international condemnation and raised questions about Crown Prince Mohammed's ability to shepherd the kingdom through a period of far-reaching social and economic reform. Here are the five worst-performing stock indexes across the globe:

Venezuela -94.89%

Venezuelan President and presidential candidate Nicolas Maduro attends the closing rally of his campaign ahead of the weekend's presidential election, in Caracas, on May 17, 2018. JUAN BARRETO | AFP | Getty Images

The worst stock market performer in U.S. dollar denominated terms in 2018 was Venezuela. The crisis-stricken country saw its IBVC index collapse more than 94 percent, as President Nicolas Maduro attempts to end a prolonged period of economic turmoil in the oil-rich but cash-poor nation.

Argentina -50.2%

People are reflected on a window of a currency exchange in Buenos Aires' financial district, Argentina, September 3, 2018. Marcos Brindicci | Reuters

Argentina struggled to cope with yet another financial crisis in 2018. The South American country's stock market index closed more than 50 percent lower in 2018, after Buenos Aires found itself at the epicentre of an emerging markets financial spiral. The emerging markets have been hurt by U.S. Federal Reserve rate hikes, which have driven up the value of the dollar versus other currencies, making it more expensive to repay dollar-denominated debt. Trade wars have also been a factor, and they hurt commodity prices. Commodities are important revenue sources in emerging markets.

Turkey -43.35%

A vendor sells Turkish national flags in Eminonu Square on the European side of Istanbul on January 4, 2018. BULENT KILIC | AFP | Getty Images

As Argentina's currency suffered last year, other emerging markets' currencies fell in sympathy — with Turkey's lira also registering steep losses. Policy disagreements between the Turkish President Recep Tayyip Erdogan and his central bank gave rise to market nerves and, complicating matters further, Turkey's detention of American pastor Andrew Brunson was a source of ongoing tension in 2018. Souring relations between Washington and Ankara initiated a rout in Turkish assets, before Brunson was eventually released in mid-October. The country's stock market index fell more than 43 percent in U.S. dollar denominated terms.

China -28.64%

President Donald Trump (L) shakes hand with China's President Xi Jinping at the end of a press conference at the Great Hall of the People in Beijing on November 9, 2017. Fred Dufour | AFP | Getty Images

China's Shanghai composite index lost more than a quarter of its value in 2018, as trade tensions with the U.S. took hold. President Donald Trump and Chinese leader Xi Jinping declared a 90-day cease-fire at the start of December, but external observers remain deeply skeptical about the chances of Washington and Beijing agreeing to a comprehensive trade pact in the proposed timeframe.

Pakistan -28.07%

Pakistan Prime Minister Imran Khan at the ceremony for the Kartarpur Corridor on Nov. 28, 2018. ALI | AFP | Getty Images