1-Two types of prepositions (A-simple one means:only the preposition as a , di,da,in ,su -- con,per, fra,or tra the same). (B-Articulated prepositions which means the definite article connected to prepositions in one word,prepositions consists of 2 letters can be joined to the different definite articles,da becomes dal, dalla, dall', dai, dagli, dalle. prepositions of 3 letters can not be connected the different articles.(rarely con) 2-Thus da+il=Vengo dal Messico --- da+la=dalla Francia --- da+l'=dall'Italia --- da+gli=dagli Stati Uniti-da+le=dalle Filippine.

In italian, countries have a gender (masculine or feminine) just like nouns. You have to adjust the preposition with the country that follows. DALL' is only used when the country starts by a vowel. "dall'Argentina" "dall'Inghilterra" "dall'India" DALLA is used when the country is feminine/starts by a consonant. "dalla Spagna" "dalla Cina" "dalla Thailandia" DAL is used if the country is masculine. "dal Belgio" "dal Perù" "dal Vietnam"