The missile attack by the Tigray People's Liberation Front on Eritrea in mid-November transformed an internal Ethiopian crisis into a transnational one. In the midst of escalating internal conflict between Ethiopia's northernmost province, Tigray, and the federal government, it was a stark reminder of a historical rivalry that continues to shape and reshape Ethiopia.
The rivalry between the Tigray People's Liberation Front and the movement which has governed Eritrea in all but name for the past 30 years - the Eritrean People's Liberation Front - goes back several decades.
The histories of Eritrea and Ethiopia have long been closely intertwined. This is especially true of Tigray and central Eritrea. These territories occupy the central massif of the Horn of Africa. The Tigrinya are the predominant ethnic group in both Tigray and in the adjacent Eritrean highlands.
The enmity between the Tigray People's Liberation Front and the Eritrean People's Liberation Front dates to the mid-1970s, when the Tigrayan front was founded in the midst of political turmoil in Ethiopia. The authoritarian Marxist regime - known as the Derg (Amharic for 'committee') - inflicted violence upon millions of its own citizens. It was soon confronted with a range of armed insurgencies and socio-political movements. These included Tigray and Eritrea, where the resistance was most ferocious.
The Tigrayan front was at first close to the Eritrean front, which had been founded in 1970 to fight for independence from Ethiopia. Indeed, the Eritreans helped train some of the first Tigrayan recruits in 1975-6, in their shared struggle against Ethiopian government forces for social revolution and the right to self-determination.
But in the midst of the war against the Derg regime, the relationship quickly soured over ethnic and national identity. There were also differences over the demarcation of borders, military tactics and ideology. The Tigrayan front eventually recognised the Eritreans' right to self-determination, if grudgingly, and resolved to fight for the liberation of all Ethiopian peoples from the tyranny of the Derg regime.
Each achieved seminal victories in the late 1980s. Together the Tigrayan-led Ethiopian People's Revolutionary Democratic Front and the Eritrean front overthrew the Derg in May 1991. The Tigrayan-led front formed government in Addis Ababa while the Eritrean front liberated Eritrea which became an independent state.
But this was just the start of a new phase of a deep-rooted rivalry. This continued between the governments until the recent entry of prime minister Abiy Ahmed.
If there's any lesson to be learnt from years of military and political manoeuvrings, it is that conflict in Tigray is unavoidably a matter of intense interest to the Eritrean leadership. And Abiy would do well to remember that conflict between Eritrea and Tigray has long represented a destabilising fault line for Ethiopia as well as for the wider region.
Reconciliation and new beginnings
In the early 1990s, there was much talk of reconciliation and new beginnings between Meles Zenawi of Ethiopia and Isaias Afeworki of Eritrea. The two governments signed a range of agreements on economic cooperation, defence and citizenship. It seemed as though the enmity of the liberation war was behind them.
Meles declared as much at the 1993 Eritrean independence celebrations, at which he was a notable guest.
But deep-rooted tensions soon resurfaced. In the course of 1997, unresolved border disputes were exacerbated by Eritrea's introduction of a new currency. This had been anticipated in a 1993 economic agreement. But in the event Tigrayan traders often refused to recognise it, and it caused a collapse in commerce.
Full-scale war erupted over the contested border hamlet of Badme in May 1998. The fighting swiftly spread to other stretches of the shared, 1,000 km long frontier. Air strikes were launched on both sides.
It was quickly clear, too, that this was only superficially about borders. It was more substantively about regional power and long standing antagonisms that ran along ethnic lines.
The Eritrean government's indignant anti-Tigray front rhetoric had its echo in the popular contempt for so-called Agame, the term Eritreans used for Tigrayan migrant labourers.
For the Tigray front, the Eritrean front was the clearest expression of perceived Eritrean arrogance.
As for Isaias himself, regarded as a crazed warlord who had led Eritrea down a path which defied economic and political logic, it was hubris personified.
Ethiopia deported tens of thousands of Eritreans and Ethiopians of Eritrean descent.
Ethiopia's decisive final offensive in May 2000 forced the Eritrean army to fall back deep into their own territory. Although the Ethiopians were halted, and a ceasefire put in place after bitter fighting on a number of fronts, Eritrea had been devastated by the conflict.
The Algiers Agreement of December 2000 was followed by years of standoff, occasional skirmishes, and the periodic exchange of insults.
During this period Ethiopia consolidated its position as a dominant power in the region. And Meles as one of the continent's representatives on the global stage.
For its part Eritrea retreated into a militaristic, authoritarian solipsism. Its domestic policy centred on open-ended national service for the young. Its foreign policy was largely concerned with undermining the Ethiopian government across the region. This was most obvious in Somalia, where its alleged support for al-Shabaab led to the imposition of sanctions on Asmara.
The 'no war-no peace' scenario continued even after Meles's sudden death in 2012. The situation only began to shift with the resignation of Hailemariam Desalegn against a backdrop of mounting protest across Ethiopia, especially among the Oromo and the Amhara, and the rise to power of Abiy.
What followed was the effective overthrow of the Tigray People's Liberation Front which had been the dominant force in the Ethiopian People's Revolutionary Democratic Front coalition since 1991.
This provided Isaias with a clear incentive to respond to Abiy's overtures.
Tigray's loss, Eritrea's gain
A peace agreement between Ethiopia and Eritrea, was signed in July 2018 by Abiy and Eritrean President Isaias Afeworki. It formally ended their 1998-2000 war. It also sealed the marginalisation of the Tigray People's Liberation Front. Many in the Tigray People's Liberation Front were unenthusiastic about allowing Isaias in from the cold.
Since the 1998-2000 war, in large part thanks to the astute manoeuvres of the late Prime Minister Meles Zenawi, Eritrea had been exactly where the Tigray People's Liberation Front wanted it: an isolated pariah state with little diplomatic clout. Indeed, it is unlikely that Isaias would have been as receptive to the deal had it not involved the further sidelining of the Tigray People's Liberation Front, something which Abiy presumably understood.
Isaias had eschewed the possibility of talks with Abiy's predecessor, Hailemariam Desalegn. But Abiy was a different matter. A political reformer, and a member of the largest but long-subjugated ethnic group in Ethiopia, the Oromo, he was determined to end the Tigray People's Liberation Front's domination of Ethiopian politics.
This was effectively achieved in December 2019 when he abolished the Ethiopian People's Revolutionary Democratic Front and replaced it with the Prosperity Party.
The Tigray People's Liberation Front declined to join with the visible results of the current conflict.
Every effort to engage with the Tigrayan leadership - including the Tigray People's Liberation Front - in pursuit of a peaceful resolution must also mean keeping Eritrea out of the conflict.
Unless Isaias is willing to play a constructive role - he does not have a good track record anywhere in the region in this regard - he must be kept at arm's length, not least to protect the 2018 peace agreement itself.