It would be a mistake to interpret the ways of imposition of new order in Europe as some deliberate acts of vengeance forced upon fallen Internationale - on the contrary, Tsar Peter IV. listened to many voices showing concerns about post-war stability in Western, Central or Southern Europe. Therefore, when French had to accept such king as Charles XI., Italians enjoyed more actual freedom, territory and investments than ever before. Carlist '
Jefe' of Spain had to endure only Russian Gibraltar, otherwise he could pursue independent foreign policy as much as the Empire didn't care about 'domestic issues' of Spain. All in all, peace in Europe in 1945 looked like a lot like if the Russian Empire decisively won three decades ago - annexation of Galicia-Lodomeria, Polish parts of Germany or previous conquest of Constantinople clearly showed this.
The so called 'Kingdom of Czechs and Slovaks' could be considered the model buffer state: it's population fiercely loyal to it's liberators and mountainous terrain ensured the order in Central Europe. When any Polish, Hungarian or German uprising happened, Czechs and Slovaks proved their worth. Syndicalist regime wasn't missed - French refusal to accept unification of Czech and Slovak lands, which was designed by nationalists since 1910s and unpopular reforms, same as coal and food confiscated by the Internationale for war effort, made leftists more hated than all previous 300 years of Habsburg rule.
Of course, many Russian soldiers had absolutely no idea what to think about Czechs: they all greet them with flowers and beers, Bohemian flags alongside the Russian ones on every corner of every city. So different from the well-known stern, cold faces of Czech legionnaries who stayed in Russia since the Great War. Being Panslavists greater than Russian themselves, they were more insulted by Russian general who thought Vltava is Danube, than by the fact, that their entirely new nation state was designed in the Winter Palace and literally given to one Romanov Prince, who himself had little interest in politics.
Prince Roman Petrovitch of Russia was the descendant of ultraconservative Tsar Nicholas I., but showed a little inclinations towards traditional Autocracy: which is probably the reason, why he was picked as a King for Czech and Slovaks, voluntarily choosing to be rather a symbol of unity than active sovereign ruler, intervening only if truly necessary, with support of the masses in the streets. During his reign, Czech and Slovaks developed a unique kind of 'military democracy', in which only active soldiers could vote representatives of the state. This later led to election of deceased King's second son Dimitri, instead of unpopular firstborn Nicholas - the move which wasn't opposed by the Empire, as before that, he dared to publicly question succession to Russian throne.
His regnal name, 'Ottokar III.' clearly revealed the expectations of Czech nationalists, as the last Ottokar, called 'The Iron and Golden King', ruled Bohemia at the peak of Czech power within the Holy Roman Empire. Indeed, in following decades, Czech and Slovak lands changed into military and technological powerhouse, maintaining peace in Central Europe - one million soldiers with thousands of armored vehicles available at any time and it's medium-range ballistic missiles allowed the Empire to focus elsewhere in the world. Be it Hungarian Uprising of 1953 or German Troubles of 1960s-1970s, a single Russian imperial soldier was unnecessary here.
Romania had little luck in 20th century: defeated and occupied in the Great War, it only experienced fall of monarchy, Iron Guard rise and fall, syndicalist revolution, another defeat and brief restoration of monarchy, replaced by syndicalist regime again, only to be a battlefield for a years between the two superpowers. With it's industry and agriculture completely destroyed, great portion of population dead and displaced, the Romanians were more than thankful to unite at last with the Transylvania and Banat, with overwhelming Romanian majority.
The Iron Guard survived the war and Ion Antonescu as the Prime Minister and Horia Sima as a Chairman of the Party held the most power in a reconstituted country - which was limited only by the King Carol II. and later his son Michael, who counted on conservative elements of society, bolstered by the Romanian Orthodox Church, which received a much support from powerful Faith and Nation movement in Russia.
Unlike such happy countries (under circumstances), the Serbia presented an opportunity for Russia to express a disgust for the ones expecting a lot now: instead, Serbia was put back to it's place as a small, poor, unimportant rural state, which had no guarantee whatsoever now from Russian Empire. The Tsar considered them unreliable 'pseudo-allies', unable to keep peace in their own place.
Montenegrin House Petrovic-Njegos also replaced the House Karadordevic in person of new King of Serbia, Mihailo II. During the coronation, he warned against any unwise moves from some elements of Serbian society, as his accession to the throne was fully backed by the Tsar of all the Russias and any deviation from this course may lead to re-imposition of order - a necessary warning in a country and public comfortable with regicides in 20th century - even before the Great War.
Fate of the rest of the lands around Danube was a more tricky: it seemed that only two options were available, three or four new states or just the one, under Habsburg rule.
Otto von Habsburg wasn't the only option for reconstructed Danubian monarchy, but his marriage to Kira Kirillovna Romanov and his firm anti-syndicalist stance before, during and after the war, helped his influence in the Winter Palace. When he was asked about Russia after his return to Vienna, Otto described it as the kind of 'beautiful and polished Greek Underworld'.
Although retaining the name of pre-war reformed monarchy, Kaiser Otto had to replace the constitution with a lot more conservative one, giving more powers to himself and nobility. Federal monarchy could stay stable as long as Austria and enlarged Croatia-Slavonia sided with the Crown against Hungarians - after they suffered worst territorial and population losses in their history and were reduced to subservient status in recreated Habsburg monarchy.
Without it's Czech industrial heartland, the Habsburg monarchy never again rose as a Great Power: barely holding back any irredentist attempts of Romanov cadet branch ruling the Italy and violent nationalist terrorism in Bosnia and Hungary from spreading, survival of the rump monarchy was the only primary goal.
Germany, on the contrary, offered many more options. Russian Empire's borders on Elbe with Berlin within? Return to 18th century? Occupy them indefinitely? Technically, German Union was never recognized by Russia and formal declaration of war against already defeated German Empire was a preventive measure to secure strategic areas. But the enemy in the Great War had to be punished: all colonies lost, some eastern lands annexed to Russia and they had to accept a new Kaiser from the another dynasty.
Grand Duke Boris Vladimirovich of Russia was a known for his restless behavior and as a notorious playboy. Also an Anglophobe, which all made him an apparently a perfect candidate for Kaiser of Germany, as is other closest connection to it was his ancestor Frederick William III. of Prussia, whose daughter married Tsar Nicholas I.
Thankfully, Boris as the 'Wilhelm V' (with Wilhem III. dead by malaria and his son Wilhelm IV. soon murdered after capture by syndicalist forces in Africa), himself quickly realized his own role in Germany as merely a figurehead to ensure a loyalty of it's people to their Russian 'liberators', with surviving and returning conservatives happy enough from mere survival of united Reich, which, they assumed, had still chance to rise again one day.
And who became the new Chancellor? Eccentric leader of Thule Society, a German occultist group which managed to survive and grow in times of German Union, as it was considered too obscure and ridiculous group of few philosophers and neo-pagans - it had no link to monarchy or conservative forces. Thule Society's clubs grew in many cities and slowly gathered an intel about leftist and other subversive organisations in Germany, mainly Jewish and liberal ones - which were put into good use, when the time came to purify German institutions by imperial agents.
Greatest fleet in the history of the world was assembled to liberate Britain - and to show the Russian Tsar that now just English-speaking Entente had enough power to fight.
The immense growth of power of Russian Empire horrified all remaining alliances in the world - especially the Anglo-American Entente, which was willing to cooperate even with the South American left-wing regimes, which started to turn away from totalism, eventually reforming into progressive democratic socialist states. People of Americas starting to realize what was at stake now. First move was the liberation of Africa and Britain from syndicalism and containing the Renewalist Russian threat.
The Tsar, of course, didn't count entirely on the skills of monarchs or political machinations within each country - elite guard divisions were prepared to intervene at any time.
'Operation Sovereign' was launched at June 6th, 1945. Canadians and Americans stormed the English beaches, encountering only a token resistance from starved and demoralized Unionist militias. Desperate population in most of the cities was revolting, with Union Jacks greeting the royalists.
In fact, syndicalist resistance was torn apart too easily, so it allowed one division of Foreign Legion to land in Dover - though stopped in East Anglia,they managed to take a London before Canadians. Soon, the captured pieces of syndicalist country were handed over to Russian imperial forces, which continued to occupy them in spite of British protests - which was the only thing they could do now.
When the Empire's war machine turned to the Chinese borders, the new territories here were properly made an imperial governorates.
Necessary infrastructure in the Far East could be rebuilt very quickly, due to recent boosts to available workforce which demanded little to maintain.
Tower built for Russia's first nuclear test: originally intended for usage as a superweapon to ensure Empire's survival in case of two or three front war, now, it could spread the fear and imposition of order whenever and wherever Tsar wanted it to happen. Test occured at September 8th, 1945 - next bombs were delivered directly to Russian Imperial Air Force. When the time came, the only Syndicalist state in war with Russia was the Ireland. But Tsar demanded war test still, to know exact effectiveness against various targets. Especially when his agents delivered a reports about Anglo-American project of same nature.
Meanwhile, development of a new weapon continued, along with new rocket engines - unlike bombers, supersonic rockets always must go through, was the assumption.