Why do you think no one can still state with 100% accuracy who started the war in August 2008? Because in reality no one knows who fired first, and there is a reasonable assumption that this was done by foreign special services and then uncontrolled processes began.
Summary
Russian obligations under the 1994 Budapest Memorandum have nothing to do with the internal conflict in Ukraine. The loss of territorial integrity by the state [of Ukraine] occurred as a result of internal processes.
Disproof
Recurring pro-Kremlin disinformation narrative about the war in Ukraine, claiming that only Ukraine and the two pro-Kremlin illegal separatists territories are warring sides in the Donbas conflict and that Russia is not part of the conflict. Consistent with pro-Kremlin disinformation alleging Russia has not violated the 1994 Budapest Memorandum.
The war in Ukraine is not an internal conflict between Ukrainians but a well-documented act of aggression by Russian armed forces, ongoing since February 2014.
There is irrefutable evidence of direct Russian military involvement in Eastern Ukraine, in the Donbas. See also the UN International Criminal Court material here. Russia is supporting its proxies with weapons, its active-duty soldiers serve there and its top military commanders visit the war zone to coordinate joint efforts with the separatists. Moreover, Moscow illegally provides weapons to the separatists. This is a well-established fact, although Russia denies it despite the fact that Russian President Vladimir Putin admitted Russia's military presence in Ukraine in 2015.
Pro-Kremlin media outlets have repeatedly tried to downgrade the significance of the Budapest Memorandum. The mentioned Budapest Memorandum is a document signed in December 1994 by Ukraine, Russia, the United States and the United Kingdom. Under the Memorandum, Ukraine agreed to remove all Soviet-era nuclear weapons. In return, the US, the UK and Russia signed the Memorandum with guarantees of the territorial integrity and sovereignty of Ukraine. According to the document, all signatory countries have to respect Ukraine's sovereign rights for its territories.
Notable is the second paragraph of the Memorandum which states that the signatories "reaffirm their obligation to refrain from the threat or use of force against the territorial integrity or political independence of Ukraine, and that none of their weapons will ever be used against Ukraine." That is, through the Budapest Memorandum, Russia pledged not to use any weapons against Ukraine.
In this regard, Russia's illegal annexation of Crimea in 2014 and the Kremlin's support of separatists in eastern Ukraine are a clear violation of the international memorandum.
The European External Action Service has also noted that Russia violated several agreements by its actions against Ukraine, including the Budapest Memorandum.
Read our recent articles on 7 myths of pro-Kremlin disinformation about the Russian military buildup near Ukraine, and Kremlin fabricated pretexts for further invasion to Ukraine.