Normally, when you say you are "in" a country or continent, Italian uses the simple preposition in without an article (e.g., in Italia, in Europa). However, as soon as you add an adjective or specific detail to describe a region or era, you must include the definite article.
Vowel-Starting Countries and Continents
Since many continents and countries start with a vowel, you will frequently combine in + l' to form nell'.
| We live in Western Europe. | Abitiamo nell'Europa occidentale. |
| In Eastern Europe, people drink a lot of tea. | Nell'Europa orientale si beve molto tè. |
Adjectives like settentrionale (northern) and meridionale (southern) also trigger the use of the article.
| I work in North America. | Lavoro nell'America settentrionale. |
| In Southern Italy, summer is very long. | Nell'Italia meridionale l'estate è molto lunga. |
Consonant-Starting Countries
If the country starts with a consonant, use the articulated preposition based on its gender. For most countries, which are feminine, in + la becomes nella.
| We spent our vacation in Northern Greece. | Abbiamo trascorso la vacanza nella Grecia settentrionale. |
| The territory in Northern France is flat. | Il territorio nella Francia settentrionale è pianeggiante. |
Modified Countries as Subjects
Just like unmodified countries, modified countries always take a definite article when they are the subject of a sentence.
| Western America is very mountainous. | L'America occidentale è molto montuosa. |
| The peninsula is flat, but southern Greece is mountainous. | La penisola è pianeggiante, ma la Grecia meridionale è montuosa. |