Put upon over the centuries by more powerful neighbors claiming their land, notably Russia, Poland and the Austro-Hungarian Empire, Ukrainians have rarely had firm allies or even their own functioning state, a situation that has encouraged a highly transactional approach to foreign and also domestic affairs.

Unlike Russia, ruled since the time of Ivan the Terrible in the 16th century by a single, strong leader, usually a tyrant, Ukraine has always been a land of competing power centers. This has made it a fertile ground for democracy but also left it a highly fractured nation with an ever shifting constellation of feuding power-brokers who often look to foreigners for help in their internal struggles.

The whistle-blower’s complaint released on Thursday revealed how Mr. Giuliani, Mr. Trump’s personal lawyer, played into this dynamic, focusing his efforts to get Mr. Biden and his son investigated on a group of senior law-enforcement officials in Ukraine who had been locked for months in a bitter turf war with rival factions within the same state structure.

The officials Mr. Giuliani sought out in the name of fighting corruption were engaged in a long feud with Ukraine’s National Anti-Corruption Bureau. The bureau, which has worked closely with the F.B.I. and was set up in 2014 with strong support from the Obama administration, is one of the few government agencies in Ukraine that Western diplomats in Kiev view as reasonably honest and competent.

Mr. Giuliani has his own business history in the country as well. More than two years ago, his company, Giuliani Security and Safety, signed a contract with a wealthy Ukrainian, Pavel Fuks, to consult on emergency planning in Mr. Fuks’s hometown, Kharkiv.

At the time, Mr. Fuks and others had become entangled in a complicated $1.5 billion deal to buy Ukrainian government bonds. In an investigation, Al Jazeera reported that the real sellers were sanctioned former insiders in the government of the disgraced former president of Ukraine, Viktor F. Yanukovych.