The Arabs are almost strong enough to conquer Western Europe

The Roman Empire existed for some 1000 years before it fell. Modern Europe has dominated the world for far less time, perhaps since the reconquest of Spain and discovery of America in 1492: about 500 years. Since 1945, Europe has been weaker, but it has continued to exercise massive influence over the world.
The fall of Rome was not something one could have easily predicted.  Standards of living in Rome far exceeded anything that could be found in its neighbours. Roman army barracks on the borders had piped running water, fountains, baths with underfloor heating.  Slavery had been ended. All Romans were citizens.  And yet the Romans were no longer able to repulse invasions and their armies had become reliant on non-Roman troops and ineffective.

The Ancient Egyptian pharaonic kingdoms were undefeated for even longer than the Romans: some 2,000 years.  However it would appear that sometime in around 1600 BCE a group of tribes, possibly from Canaan successfully and unexpectedly conquered Egypt.

Western Europe is far more vulnerable than would appear from pure economic data. While it dominates the global economy and exercises massive influence everywhere, Western Europe has systematically neglected its military and simply relies on the USA to protect it from the outside.

To make this point, I have taken the four largest military powers in Western Europe and compared them to four large Arab states (all Sunni except Syria which has a Sunni majority), using data from the globalfirepower website.
I have not included Iran which is not Arab but has massive military power. Were Syria and Iraq to be combined they would be a formidable power and there are no European countries (except Russia) which can rival these countries in military terms. Turkey is arguably more powerful than any of the countries listed below but is Islamic and in NATO, so in a sense it keeps the balance of power.

For comparison purposes I have added Israel, which is almost as strong as Turkey (not in active military forces).

What you can see is that on land the balance is clearly shifting in favour of the Arabs.

	Germany	France	Britain	Italy	Europe 4	Israel	Arab 4	Algeria	Egypt	Syria	Saudi Arabia
Soldiers (active) in thousands	180	202	146	320	848	160	1391	512	468	178	233
Soldiers (reserve) in thousands	180	195	82	42	499	630	1795	400	800	570	25
Tanks	408	423	407	586	1824	4170	11275	975	4600	4500	1200
Artillery	150	550	227	256	1183	950	6360	600	2200	2580	980
Missile systems	50	44	42	21	157	48	2601	148	1481	650	322
Combat Planes	297	540	249	270	1356	484	1730	188	811	340	391
Combat Helicopters	34	46	65	59	204	48	117	35	36	28	18
Ships	77	103	55	168	403	61	408	56	241	56	55
Submarines	4	10	10	6	30	5	8	4	4	0	0
aircraft carriers	0	0	1	2	3	0	0	0	0	0	0

What is missing in this chart is nuclear power which is a potential game breaker and economic power, with its implied military potential where Europe is more powerful than anyone.
Even so, it does show just how limited European military power is and that, if this trend continues, Europe could become vulnerable particularly if it loses its USA backing and its (possibly quite small) nuclear option is neutralized in some way.

If you think Europe can easily power-up then bear in mind that it takes a lot of time to train military personnel - especially commanders - and that the skills and know-how associated with warfare are gradually being lost.