Step 1: Recall the timeline:
In February 2022, Russia began a full-scale invasion of Ukraine. Before that, Russia had demanded that Ukraine never join NATO.
Step 2: Test each option against the facts:
Oil purchase from UAE: no record, and no link to security. Leadership change in Russia: not true. Friendship with USA: true in a general sense, but it is the weaker, broader claim.
Step 3: Choose the direct cause:
The clear and specific reason cited by Russia was NATO expansion, shown by Ukraine's plan to join it.
Step 4: Answer:
So option 1 is correct.
Final Answer:
Option 1 matches the main reason cited by Russia.
\[ \boxed{\text{1 (Ukraine's intention to join NATO)}} \]