Doing a quick search, I couldn't find anything to back this up, hence the low confidence rating, but in the context, I think this might be the idea.

pamphlet
2. a short treatise or essay, generally a controversial tract, on some subject of contemporary interest:
a political pamphlet.
http://www.dictionary.com/browse/pamphlet

Political Pamphlet
MICHAEL GALCHINSKY
...
Extract

The political pamphlet's primary purposes are not to teach and delight, but to protest and incite. Critics have long struggled with whether and how to interpret this genre as a literary form. George Orwell described the challenge well: ‘To ask “What is a pamphlet?”’ he wrote, is rather like asking ‘What is a dog?’ We all know a dog when we see one, or at least we think we do, but it is not easy to give a clear verbal definition, nor even to distinguish at sight between a dog and some kindred creature such as a wolf or a jackal. The pamphlet is habitually confused with other things that are quite different from it, such as leaflets, manifestoes, memorials, religious tracts, circular letters, instructional manuals and indeed almost any kind of booklet published cheaply in paper covers. The true pamphlet, however, is a special literary form. ( Orwell 1948 : 7)
http://www.blackwellreference.com/public/tocnode?id=g9781405...

Suggestion.

https://www.google.com/search?ei=0SozW6OOL-nIgAb58bvIAw&q="p...

"Impresos", in principle, refers to any printed matter. In practice, it probably does mean mostly pamphlets, particular if we interpret "pamphlet" is a broad sense as any short polemical publication. Nevertheless, I think that is too narrow a term, when you look at the range of political printed matter in this context (early nineteenth-century revolution in Peru and Latin America generally).

First of all, more generally, it is worth noting what "impresos políticos" means in a related context: the book Bolivia, 1825-1930: un siglo de impresos políticos, by Marta Irurozqui and Víctor Peralta Ruiz (1997), not least because Víctor Peralta is one of the major researchers on the Peruvian context. The authors define the scope of their work as follows:

"Se ha procurado reunir en esta bibliografía la copiosa e importante folletería, libros y demás impresos de carácter político que se publicaron en Bolivia entre 1825 y 1930"
https://books.google.es/books?redir_esc=y&hl=es&id=K6njAAAAM...

So books and pamphlets are "impresos", but there are other kinds too.

Then again, various discussions of "impresos" in Peru in 1808-1814 actually refer to press publications: newspapers. So newspapers are also "impresos". Your text distinguishes them — "la prensa y los impresos políticos" — but it should really have said "la prensa y otros impresos políticos", as Domingo Morán (another major researcher who has closely studied the Peruvian press of this period) does here:

" Juan Canter utilizó periódicos y otros impresos políticos con la intención de entender la configuración política y literaria de las sociedades secretas de la época revolucionaria "
http://www.iri.edu.ar/publicaciones_iri/IRI COMPLETO - Publi... (p. 3).

In another article, Morán gives us an idea of the range of "impresos políticos" in Lima and Río de la Plata in this period; they notably include sermons, which are mentioned in several other places as vehicles of revolutionary ideas:

"La acelerada politización de los actores sociales en Lima y el Río de la Plata a partir de la coyuntura de la crisis hispana tuvo en la difusión de la prensa y los impresos políticos un elemento esencial. Así, durante estos años se produce el surgimiento de una diversidad de periódicos, folletos, sermones, hojas sueltas, pasquines y correspondencia, que permiten captar el desarrollo del ciclo revolucionario en América y los balbuceantes orígenes de la opinión pública (Molina, 2009 y Pimenta, 2011)."
https://csonline.ufjf.emnuvens.com.br/csonline/article/downl...

And in yet another article, Morán shows that Peruvian political literature of the period included "periódicos, papeles, folletos, libros", refers to "periódicos, sermones y otros impresos", and even gives a list which appears to distinguish "impresos" from pamphlets, newspapers and books: "impresos, panfletos, periódicos, libros, etc."
http://historiapolitica.com/datos/biblioteca/prensa y pol XI...

In short, "impresos" could be more or less any kind of printed matter with political content and is used to apply to different kinds in different places. It's a catch-all term and calls for a catch-all translation. I honestly think the best bet is to call them publications, along the lines of the following reference, referring to a different context:

"Under the heading “Revolution and Counterrevolution in Guatemala: 1944-1963,” the Benson Collection has gathered nearly 3,000 political publications widely circulated in Guatemala during this tumultuous period. The variety of manifestos, satirical cartoons, party pamphlets, and other forms of “street literature” provided the rare opportunity to examine how Guatemalan power-contenders framed issues and attempted to gain popular support."
http://cllas.uoregon.edu/grant-opportunities/2016-grant-reci...