Covertly supported by expeditionary forces from Uganda, Ethiopia, and Eritrea, the SPLA's offensive was a major success, with several SAF garrison towns falling to the South Sudanese rebels in a matter of days.

At the same time, a large group of WNBF fighters as well as SAF, FAZ, and ex-Rwandan Armed Forces soldiers was trying to escape from Zaire to Yei.

Following this victory, the South Sudanese rebels continued their offensive until late April, capturing several other towns in Equatoria and preparing further anti-government campaigns.

The success of Operation Thunderbolt significantly strengthened the SPLA in Western Equatoria, and weakened the Sudanese government's control over its southern territories.

In 1983, revolutionaries and separatists from the country's mostly Christian-Animistic south banded together and launched an insurgency against the government which was traditionally dominated by Muslim elites from the north.

[4] Negotiations between the government and the SPLA almost resulted in a peaceful solution of the conflict, but ended after the 1989 coup d'état which brought the National Islamic Front (NIF) under Omar al-Bashir to power.

[10][11] At the time, the South Sudanese separatists were weakened by internal divisions and the collapse of the People's Democratic Republic of Ethiopia, their most important foreign ally.

Though the country's old, pro-SPLA leadership had been overthrown during the Ethiopian Civil War, Ethiopia's new government under Meles Zenawi was undermined by Sudan, and consequently decided to aid the South Sudanese separatists.

[6] This belief was not based on hard facts, but an assumed personal connection between SPLA leader John Garang and Ugandan President Yoweri Museveni.

[25] In an effort to topple Museveni's government, Sudan thus supported and even organized several Ugandan insurgent groups from 1986, though the extent to which these rebels actually followed Sudanese orders varied greatly.

[26][27][28] They were generally based in southern Sudan or eastern Zaire (present-day DR Congo), whose dictator Mobutu Sese Seko tolerated their presence out of enmity toward Museveni.

[30][31] Furthermore, the conflict along the Sudanese-Ugandan-Zairean border intensified, as not just the various rebel factions but even the Sudanese and Ugandan militaries launched cross-border raids and bombardments.

[11][32][33] This volatile situation further escalated upon the outbreak of the First Congo War in 1996, as an alliance of rebel groups and states led by Rwanda invaded Zaire to topple Mobutu.

[39] The SPLA enjoyed strong support by foreign states, namely Uganda, Ethiopia, and Eritrea, during the preparation and execution of Operation Thunderbolt.

For Uganda, Operation Thunderbolt's main aim was to capture the entire border to block the SAF from advancing into Zaire to help its allies there.

[1][45] The assault on Kaya was preceded by an artillery bombardement,[51] and spearheaded by the Uganda People's Defence Force with tanks, howitzers, mortars, and machine guns.

A task force of UPDF tanks led by Hannington Kyazze crossed a nearby river, and attacked Kaya from the rear.

[49] The SAF had previously realized that the SPLA was preparing an offensive, but the rebels managed to capture Kaya on the first day of the attack nonetheless,[45][50] while the UPDF seized the strategically important nearby Koboko Mountain.

[53] On 10 March, the SPLA and UPDF captured Bazi and Gumuni,[45][50][49] while the Sudanese and Ugandan militaries reportedly exchanged artillery fire across their common border.

[50] The important town of Kajo-Kaji was taken by the South Sudanese rebels and UPDF on 24 March,[50][52] and a SAF counter-attack along the Yei-Juba road was repelled two days later.

When the SPLA forces under Salva Kiir Mayardit's command managed to cross the river, however, they launched "lightning strikes" against the next Sudanese bases.

[60] However, an initial attack by the SPLA and UPDF on the strategically important Jabelein area, 39 miles (63 km) from Juba, partially failed.

[40][42][62][63] The SPLA claimed to have put 8,000 enemy troops "out of action" during Operation Thunderbolt,[50] including a large number of Sudanese senior officers.

[31] The rebel group had also seized a large amount of small arms, ammunition, landmines, and heavier equipment such as artillery pieces, at least 60 tanks,[43] anti-aircraft guns, and anti-tank cannons, greatly increasing its combat capabilities.

[69] Operation Thunderbolt, along with simultaneous offensives by the SPLA and other insurgents, further worsened the Sudanese government's dire shortages in manpower and equipment.

The regime was reportedly forced to resort to forcibly recruiting schoolboys, train them just 15 days, and then send them into battle with no more than a gun, a Quran page to "ward off infidel bullets", and a key to unlock Heaven's Gate if they fell in combat.

It provided the rebel group with an international propaganda boost, as it portrayed its own rule in the town as free and fair in contrast to the previous administration which was widely perceived as oppressive.

[36] Operation Thunderbolt also weakened the WNBF and UNRF (II) to a great extent, diminishing their ability to fight the Ugandan government and its allies.

As it had also suffered from internal disputes, and mass desertions, the massive defeat in Sudan meant that the WNBF's "insurgency was essentially spent by 1997".

[76] Nevertheless, the Sudanese government continued to support the remaining remnants of WNBF and UNRF (II) that had fled into the Garamba National Park.