This is a challenging question that I think has many possible and equally correct interpretations. I’ll try and discuss some of these that I find most important and maybe some others can add their own ideas.

Most simply, out of the conflict comes the Argentine nation-state. Most historians recognize that Argentina really did not exist until the 1880s. Prior to independence, there was very little national cohesion among localities. Once independence came, many diverse groups of people with differing interests began competing to fill the Spanish power vacuum. Significantly, independence came so suddenly that most of the institutions that constitute a nation had to be created on the fly. This was really what the conflict between unitarios and federales was all about. The two sides, at both the national and local level, were working out (usually violently) the form that a new state would take. Of course, they were not the only groups participating in this endeavor, but they were the ones that came out of the struggle with the most influence. Over the course of their conflict, they had to define the scope of the government, political participation within it, governmental institutions, infrastructure, and trade relationships, which were all made more complicated by the challenging historical development and the geographical realities found in region.

The unitario vs. federales conflict thus is seen by historians collectively as the vicissitudes of state formation. Out of the back and forth conflict came many of the key institutions that became so important during the twentieth century like the national army, the judicial system, the public school system that attempted to tie diverse peoples to a unified cultural narrative, and Buenos Aires’s role as the new capital and federal district. Additionally, the constitution and a push toward liberalism, although somewhat conservative and oligarchic in nature initially, opened the door for larger political participation in the twentieth century.

Another key consequence was the split between Buenos Aires and the interior provinces that resulted from the drastic change in South American trade networks. The civil wars created a huge economic shift which devastated the interior provinces but led to the growth of the agroexport economy in the Littoral and Pampean regions which proved to be Argentina’s economic engine until 1930. As a result of the widening economic gap, Buenos Aires increasingly began to think that it alone constituted the nation. The gap between Buenos Aires and the interior continued to be reflected economically and socially throughout the twentieth century.

One could also point generally, although I might also argue superficially, to the creation of a flawed government. For example, the rise of caudillos seems to foreshadow a latent militarism that sprang up now and then to replace civilian governments. The new constitution had a provision which could lead to its suspension in a state of siege, and the executive branch remained exceedingly powerful. Rosas sometimes is portrayed as a populist leader whose political mobilizations resembled those of future populist leaders. Also, Rosas’s famous Mazorca, his secret police that terrorized the populace of Buenos Aires in the 1830s and 1840s, has been pointed to as a forerunner to state terror.

One last important impact, and the one that you reference, is the great cultural influence of the nineteenth century as expressed through the split between civilization and barbarism. These ideas existed before Sarmiento, but his work Facundo perpetuated the myth throughout Argentine literature. Sarmiento and later writers like Borges struggled with the apparent contradictions in Argentine society that resulted from the conflict: the split between urban and rural, between European culture and indigenous culture, between the poverty stricken provinces and the wealthy capital, and it is this dichotomy, although simplified, that continued to bubble up in cultural and political narratives throughout the twentieth century.

So I hope I’ve been able to provide you with a few ideas. I think the most important legacy is that it is out of the conflict of state formation that Argentina as the nation we know today emerged. This is reflected politically, socially, and culturally during the twentieth century, although Argentina was also heavily shaped by the agroexport economy that ushered in prosperity during the last half of the nineteenth century and the huge influx of immigrants that would shape the modern economy. The two political parties would largely disappear before 1880, but the legacy of the conflict shaped the twentieth century heavily.