One can speculate about reasons for the U.S. to incite civil war in Ethiopia or Eritrea until the cows come home(and even if there were reasons to do so that is very weak evidence that it actually did so), but the reality is that there is no credible evidence that the U.S. has done so.
The actual causes for the civil war in question are described here and don't involve the U.S.:
Following the end of the Ethiopian Civil War in 1991, Ethiopia became
a dominant-party state under the rule of the Ethiopian People's
Revolutionary Democratic Front (EPRDF), a coalition of four ethnically
based parties dominated by the Tigray People's Liberation Front
(TPLF). The founding and most influential member was the TPLF and the
chairman was Meles Zenawi, who was the prime minister of Ethiopia
until his death in 2012. He was succeeded by Deputy Prime Minister
Hailemariam Desalegn, the chairman of the Southern Ethiopian People's
Democratic Movement (SEPDM), a coalition member. On 15 February 2018,
Hailemariam announced his resignation as both prime minister and
chairman of the EPRDF, owing to a growing discontent within the
public, fueled by a reaction to 27 years of repression.
On 28 March 2018, in a closed-door election to chair the EPRDF,
executive committee members elected the Oromo Peoples’ Democratic
Organisation (OPDO) chairman Abiy Ahmed. On 2 April 2018, Ethiopian
parliament elected Abiy as prime minister. One of Abiy's first actions
after his election was to initiate a warming of relations with
Eritrea, a long-time rival of the TPLF, to end a 20-year long border
conflict. While this decision was considered a cause of celebration at
the time, many within the Tigray Region were heavily critical of this,
seeing it as a betrayal of those who died in the 1998–2000 war. The
TPLF condemned the peace initiatives, saying they were hastily made,
had "fundamental flaws," and also claimed it was decided on without
consulting long-time TPLF members.
On 1 December 2019, Abiy merged the ethnic and region-based parties of
the EPRDF (which had governed Ethiopia for 28 years) and several
opposition parties into his new Prosperity Party. The TPLF, which had
long dominated Ethiopian politics, refused to join this new party.
After losing the election and being ousted from the federal
government, TPLF officials relocated to the Tigray Region, continuing
to administer control there while frequently clashing with the federal
government. In one instance, the Tigray regional government was
reported to have defied the federal government and refused to allow
Ethiopian Federal Police to arrest Getachew Assefa, the former chief
of the National Intelligence and Security Service (NISS) of Ethiopia
and executive member of the TPLF.
The Ethiopian government and its supporters have accused the TPLF of
trying to re-establish their rule over the country through violence
and force. In turn, the TPLF has accused the federal government
of accumulating too much power for itself, and that it was engaging in
ethnic discrimination of Tigrayans.
Throughout 2020, tensions between the federal government and the TPLF
escalated in the months leading up to November. In March, the National
Election Board of Ethiopia delayed the general elections – originally
scheduled for 29 August 2020 – to a then-undetermined date, due to the
COVID-19 pandemic. The terms of federal and regional lawmakers, as
well as the executive branch, were then extended by federal parliament
beyond the October 2020 constitutional mandates.
The TPLF, led by its chairman Debretsion Gebremichael, rejected these
measures, arguing that they were unconstitutional, and held its own
regional election on 9 September, in defiance of the federal
government. Several journalists were barred by the Ethiopian
government from travelling to cover Tigray's regional election.
Ethiopia considered the Tigray election to be illegal, and responded
by slashing federal funding to the region, a decision the TPLF
described as "tantamount to declaration of war."
In late September 2020, the TPLF stated that the constitutional term
limit of the House of Federation, the House of Peoples'
Representatives, the prime minister, and the Council of Ministers was
5 October 2020 and that for this reason, it would consider "the
incumbent" constitutionally illegitimate after 5 October; they
proposed replacing the government with a technocratic caretaker
government, as detailed in a plan posted on Facebook by the Coalition
of Ethiopian Federalist Forces. Ethiopian elite units were transported
to Gherghera base near Asmara, as part of an alleged pact between
Prime Minister Abiy and Eritrean President Isaias Afwerki to "strike
out of existence the TPLF," according to former Eritrean Minister of
Defence Mesfin Hagos.
In late October 2020, the Ethiopian Reconciliation Commission stated
that it was trying to mediate between the federal government and the
TPLF, as well as the other regional governments, but that the
pre-conditions set by all sides were blocking progress. As tension
continued to grow, a brigadier general appointed by Abiy was prevented
by the Tigray government from taking up his military post. The same
day before the Tigray forces launched the Northern Command attacks,
the federal parliament of Ethiopia had suggested designating the TPLF
as a terrorist organization.
The 1995 Constitution of Ethiopia states in Article 39.1, "Every
Nation, Nationality, and People in Ethiopia has an unconditional right
to self-determination, including the right to secession." Article 62.9
grants the House of Federation the right to "order Federal
intervention if any State [government], in violation of [the]
Constitution, endangers the constitutional order."
Certainly, no U.S. politician or senior civil servant has ever publicly called for the U.S. to incite civil war in Ethiopia or Eritrea in the time frame in which it occurred.
The U.S. does, in general, disfavor human rights violations everywhere in the world, and favors measures that are likely to end or reduce the intensity of wars with which it has only remote interests, and this can be one sided if only one side seems to be responsible for most violations of international norms.
In this case, Eritrean forces appear to have invaded sovereign Ethiopian territory without the permission of the Ethiopian government which is strongly against international norms. This seems to be what is going on in this case.