Aha! So, it is not about Bessarabia, it is about Soviet demands over Bessarabia. I think this is the core issue of numerous misunderstandings. If we start from analyzing what the Soviets demanded and see that Romania and the west did not made sufficient steps to apease it, we observe insuficient action from the side of Romania (did not organize a referendum), as well as from the west (did not succeed in overthrowing the Reds - to try is not enough). But also we run into Англия, Франция, Италия, Япония и Румыния подписали в Париже т. н. Бессарабский протокол, согласно которому они признали суверенитет Румынии над Бессарабией, и установили, что этот суверенитет "не может быть поставлен на обсуждение", which obviously ties the hands of Romania: whatever you say, it was much more important for Romania to have normal relations with the rest of the world than with Russia.
 But I said from early on, that Bessarabia, not Russia is the center of the issue. It is Bessarabians that chose this or that, not Romania or Russia. Russia had intervened only in 1940, without being invited by a local body or by MPs from Bessarabia, without even a mock support from inside Bessarabia. Why should Russia's demand be treated supperior to Bessarabia's choice (good or bad, it was a choice made in full awareness). The (military) treaty you mention was signed in February, i.e. before 27 March 1918 between two neighboring to Bessarabia countries. It can not possibly tie the hands of Bessarabia itself, by then an independent country.
 About autonomy, as far as I know, after the 27 November, resp. 1 December 1918 union of Bukovina, resp. Transylvania, a government was set for the entire united Romania, led by a Transylvanian politician (Alexandru Vaida-Voevod). He was too liberal for the phanariot-minded politicians that used to govern in Bucharest before. They tolerated "new Romanians" in government only becuse the circumstances made that necessary. Among other things, Vaida started a large campain of land reform, widely supported also by Bukovinians and Bessarabians, but very feared by the old ruling elite in Bucharest (recall the 1907 peasant uprising, still very fresh in mind). They tollerated Vaida's governments (there were 2 or 3 I think) for ca. 1 year, and in early 1920, a "black coalition" was formed, and General Averescu became prime-minister (similar to the one formed in Romania in early 2006 against Basescu, which lamenably failed within 1 month, but dragged the country more into politicianist discourse until last autumn). Land reform was limited and only went as far as to finish what was started. The new Constitution of 1923 was written by these people, who put the word "unitary" everywhere they could fit it into. Thus the autonomy of all three new provinces was not enshrined in the new Constitution. In return that led to a bitter division of the politics: on one side National-Liberal party of Bucharest old politicians, on the other the Transylvanian-dominated National-Ţărănist party. In 1928-1930, the latter started to gain momentum, and to sealed it they brought in Carol II from forced exile. But Carol II turned to be even worse, so they actually shut themselves into leg, so to say. That led some of them to more nationalistic discurse (for example Vaida himself - Dahn even calls him fascist, which is not true, but I don't want to argue with Dahn), others managed to escape this trap (for example Maniu). You see, you have to take into consideration the entire going ons. Bessarabia was left without regional autonomy because no other province got it, which in turn was because the old phanariot-mineded people carried the day in early 1920s. These people lost the grip on power, but it took time. Even in modern Romania you still have the continuation of the same disputes. On one side you have many politicians asking for setting up regions and more local autonomy (again, surprisingly many Transylvanians among them), on the other side you have the command-system-minded partly-communist-foprmed bureaucracy, who fear regionalization (again, surprizingly many Oltenians and other likes of them among). But unlike the interbelic period, it seem that now the movement is strictly oriented in one direction. Regionalization and greater local autonomy is inevitable, whether you bring the EU-standard pretext or not. So, my second part of the answer is: if it were not for the Soviet occupation, the rise of fascism, and WWII, we would have had autonomy for Bessarabia (with a powerful local legislative body) by 1950s. Communism only created a pause, things continue to roll today. \talk