In which present-day country did the Aztec civilisation flourish before the Spanish conquest?

Introduction / Context:
This question belongs to pre-Columbian American history. The Aztec civilisation was one of the great Mesoamerican cultures that developed sophisticated cities, temples and a rich religious and social life before the arrival of Europeans in the Americas.

Given Data / Assumptions:
• We are identifying the modern country that covers the core region of the Aztec civilisation. • The Aztecs built their capital at Tenochtitlan. • The question refers to the period just before Spanish conquest in the sixteenth century.

Concept / Approach:
The Aztecs lived in central Mexico. Their capital city Tenochtitlan was located on an island in Lake Texcoco, in the area now occupied by Mexico City. Because of this, any question asking where the Aztec civilisation was located expects the answer "Mexico" as the modern country name.

Step-by-Step Solution:
Step 1: Recall that the Aztecs are associated with Mesoamerica, not Europe, Africa or Asia. Step 2: Identify that their capital, Tenochtitlan, is the site of today's Mexico City. Step 3: Compare the given options and locate which one corresponds to central Mesoamerica. Step 4: Recognise that this region lies within present-day Mexico. Step 5: Choose "Mexico" as the correct option.

Verification / Alternative check:
History references on pre-Columbian civilisations almost always describe the Aztec Empire as occupying much of central Mexico at the time of Spanish contact. Maps of the Aztec Empire show it covering the Valley of Mexico and surrounding areas, further confirming that the modern country where it originated is Mexico.

Why Other Options Are Wrong:
Option Greece: Associated with ancient Greek civilisation, not Mesoamerican cultures. Option United States of America: Some ancient cultures existed in what is now the USA, but the Aztecs were based further south. Option Egypt: Known for the Nile Valley civilisation, pyramids and pharaohs, not Aztec temples. Option Peru: Associated mainly with the Inca civilisation in the Andes, not the Aztecs of Mesoamerica.

Common Pitfalls:
Students sometimes confuse Latin American civilisations such as the Maya, Aztec and Inca. A quick memory aid is: Maya (Yucatán and Central America), Aztec (central Mexico, Tenochtitlan) and Inca (Peru and Andes). Matching each civilisation to its core region helps avoid mix-ups in objective questions.

Final Answer:
Hence, the Aztec civilisation originally flourished in what is now Mexico.