I don't think we need to be too neutral here. These "entradas" were raids: the Christians went in, captured some slaves, and left. I think "incursions" is the right word. Obviously in the early sixteenth century Cisneros made some more substantial military incursions and captured a series of coastal enclaves, but apart from that the "entradas", as I say, were short-lived raids, in and out; the Christians didn't stay any longer than necessary.

At least, it will depend a bit on what the article is actually about, but the expression "entradas en Berbería" was used in the fifteenth and sixteenth century to refer to this.

As long ago as 1773, Joseph de Viera y Clavijo wrote (a propos of the Canaries):

"En el siglo octavo, y noveno (dice un célebre Autor) eran los barbaros los que hacian incursiones sobre los Pueblos civilizados : en el 15. y el 16. fueron los pueblos civilizados los que hicieron incursiones sobre los barbaros".
http://books.google.es/books?id=b28OAAAAQAAJ&pg=PA174&lpg=PA...

"Cuando Felipe II volvió a permitir las entradas en Berbería, después de haberlas prohibido en 1572 por «conveniencias políticas», una de las razones para permitir su reanudación fue, precisamente, el acopio que se hacía de esclavos negros como consecuencia de los rescates"
http://www.burbuja.info/inmobiliaria/7835177-post7.html

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Note added at 3 hrs (2013-06-12 14:31:49 GMT)
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I think either, in principle. Perhaps "Incursions of Christians" might be slightly more suitable in that these are typically isolated incidents rather than organised campaigns (and "Christian incursions" could sound a bit like religiously-motivated expeditions), but on the other hand "Christian Incursions" is neater. I think I'd choose the latter, as David suggests, but it's marginal.

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Note added at 11 hrs (2013-06-12 22:59:00 GMT)
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"Entradas" does not refer to friendly or peaceful visits; it refers to uninvited incursions. The Berbers returned the compliment, making repeated incursions into the Canaries in the sixteenth century. Naturally enough relations between Spain and North Africa during these centuries were mostly hostile, with a period of armed conflict during the early sixteenth century. There was a peaceful period under Philip II, who went out of his way to try to win the favour of the Berbers for a period in the 1560s-70s, in order to try to avoid them joining forces with the Turks. It was precisely then, during the peaceful period, that the "entradas" ceased.

So I think "incursions" is definitely the right word. As I say, "entradas" does not refer at all to peaceful visits, and the only ongoing Spanish presence in North Africa was in the enclaves captured by Cisneros, where it was maintained by armed force.

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Note added at 12 hrs (2013-06-12 23:58:01 GMT)
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The reason I've stated so categorically that the "entradas" were raids or incursions is that the term "entradas en Berbería" was used in those centuries with that meaning and is used nowadays by historians to refer to that phenomenon. It is used thus, for example, by the distinguished historian of Spanish-Moroccan relations (very pro-Franco, it must be said), Tomás García Figueras, in his article "Cabalgadas, correrías y entradas de los andaluces en el litoral africano, en la segunda mitad del siglo XV", which you can read here, if you wish (pp. 51-79). They were military raids. García Figueras rightly mentions evidence of more friendly relations at times, but that's not what "entradas" refers to.

Well now, I don't think the article you're dealing with is available online; I've only seen the title in a conference programme. But the author, Juan José Iglesias Rodríguez of the University of Seville, has spoken on this subject:

"En su charla, Juan José Iglesias catedrático de Historia Moderna de la Universidad de Sevilla, explicó las relaciones existentes entre el litoral andaluz y el litoral norteafricano en los siglos XVI y XVII, donde El Puerto tuvo protagonismo, manteniendo unas relaciones con los pueblos de dichas costas que a veces fueron pacíficas y en ocasiones violentas. En cuanto a las relaciones amistosas, destacó el conferenciante cómo entonces, al igual que en la actualidad, los pesqueros iban a faenar al norte de África (Sáhara y litoral Atlántico), y en cuanto a los contactos de tipo violentos destacó las incursiones que se producían tanto en el litoral andaluz como en el litoral africano (Berbería), por ambas partes para la captura de cautivos y el saqueo, además de le existencia del corso, bajo licencia de los reyes de Castilla, cuyas naves tenían su base en los puertos de la Bahía."
http://www.diariodecadiz.es/article/elpuerto/1446741/aula/me...

So it wasn't all hostility; they fished in each other's waters too. But I don't think he can be using "entradas" to refer to that. The phrase, as I say, is well established and denotes the usual raids. What he is apparently saying is that the famous "entradas", incursions, were not the whole story; the people on the coasts of Cadiz and Barbary were capable of getting along.

One last point. He says "entradas de cristianos", not "españoles". He is thereby invoking, I presume deliberately, the crusading element and the otherness of the Islamic Berbers vis-a-vis the Christian Spaniards. The Cadiz fishermen were Christians, but they weren't concerned with religion when they went fishing.