The Europeans didn't really react to it; both Britain and France had their own issues and weren't able to fight as it didn't seem necessary.
March 1936: Hitler remilitarizes the Rhineland, breaking rules of the treaty of Versailles; he does this in order to benefit from the strategic location of the Rhineland.
In March 1938 Germany annexes Austria as 99% of Austrians vote to join Germany; people who oppose Nazi ideology were tortured, killed, and arrested. Anti-Semitic acts follow the takeover.
Europeans don't take action; the only thing is that there are vocal protests in UK and Vatican.
September 1938 Hitler agrees to sign the Munich Agreement stating that he won't attack anymore countries; yet in soon he invaded Czechoslovakia as that was the next step in his plan towards the "greater Germany".
The Europe sighed in relief as they though this pact would work since Chamberlain was praising it; yet everyone was in a shock when Hitler took over the Sudetenland only a day after signing the pact
In May 1939 Hitler signs the Pact of Steel which means Germany allies with Italy; both countries are uncertain of each other. This pact starts the Axis powers.
The Europeans are aware of the alliance but didn't really react to it. It was on the newspapers but didn't even make a headline.
In August 1939 Germany and Soviet Union sign a Non-Aggression pact which guarantees that the countries won't attack each other within the next 10 years; the pact also states how the two powers are going to divide the Eastern Europe between them. The pact fell apart when Nazis invaded Soviet Union in June 1941.
Finally the countries started fearing for what's to come; the pact made headlines but no formal action was taken against Germany.
In September 1939 Germany invades Poland; Germany described the attack as self defense, and they also said it would be living space for Germans.
The Allies were not convinced and finally declared a war against Germany leading to World War II beginning.